The Holy Quran states:
Allah is He besides Whom there is no God, the Living, the Self-Subsisting and All-Sustaining. He has sent down to thee the Book containing the truth
andfulfilling that which precedes it; and He sent down the Torah and the Injil, before this, as a guidance to the people; and He has sent down the Discrimination (the Quran). (Al Quran 3:3-5)
Here is a 4 minute video clip about the Q document:
The discovery of the Gospel of Thomas was a watershed event in the study of Q document. Prof. Bart Ehrman explains:
Q then provided the material found in Matthew and Luke but not in Mark. It is widely assumed that Q was an actual document, written in Greek, in circulation in the early church, a document that recorded at least two deeds of Jesus (the story of Jesus’ temptations is in Q, as is an account of his healing the son of a centurion) and a number of his teachings, including the Lord’s Prayer, the Beatitudes, and other familiar sayings.
In the nineteenth century, one of the principal objections to the existence of this hypothetical lost Gospel, Q, was that it was hard to imagine-impossible for some scholars-that any Christian would have written a Gospel containing almost exclusively Jesus’ teachings. Most striking was the circumstance that in none of the Q materials (that is, in none of the passages found in Matthew and Luke, but not in Mark) is there an account of Jesus’ death and resurrection. How, asked skeptical scholars, could any early Christian write a Gospel that focused on Jesus’ sayings without emphasizing his death and resurrection? Surely
thatis what Gospels are all about: the death of Jesus for the sins of the world and his resurrection as God’s vindication of him and his mission.
This was a common argument against the existence of Q, until the Gospel of Thomas was discovered. For here was a Gospel consisting of 114 sayings of Jesus, with no account of Jesus’ death and resurrection. Even more than that, this was a Gospel that was concerned about salvation but that did not consider Jesus’ death and resurrection to be significant for it, a Gospel that understood salvation to come through some other means.
Salvation through some other means? What other means? Through correctly interpreting the secret sayings of Jesus.
The very beginning of the Gospel of Thomas is quite striking, in that it reveals the author’s purpose and his understanding of the importance of his collection of sayings and, relatedly, of how one can acquire eternal life:
These are the secret sayings which the living Jesus spoke and which Didymus Judas Thomas wrote down. And he said, “Whoever finds the interpretation of these sayings will not experience death.” (Saying 1)
The sayings recorded here are said to be secret; they are not obvious, self-explanatory, or commonsensical. They are hidden, mysterious, puzzling, secret. Jesus spoke them, and Didymus Judas Thomas, his twin brother-wrote them down. And the way to have eternal life is to’ discover their true interpretation. Rarely has an author applied so much pressure on his readers. If you want to live forever, you need to figure out what he means.
Before proceeding to an interpretation of the Gospel, an interpretation that has suddenly assumed an eternal importance, I should say a final word about Thomas in relation to the Synoptics.
No one thinks that Thomas represents the long-lost Q source. A large number of the sayings in Q are not in Thomas, and a number of the sayings in Thomas are not in Q. But they may have been similar documents with comparable theological views. The author of Q, too, may have thought that it was the sayings of Jesus that were the key to a right relationship with God. If so, in losing Q we have lost a significant alternative voice in the very earliest period of early Christianity. Most scholars date Q to the 50s of the Common Era, prior to the writing of the Synoptic Gospels (Mark was some ten or fifteen years later; Matthew and Luke some ten or fifteen years after that) and contemporary with Paul. Paul, of course, stressed the death and resurrection of Jesus as the way of salvation. Did the author of Q stress the sayings of Jesus as the way? Many people still today have trouble accepting a literal belief in Jesus’ resurrection or traditional understandings of his death as an atonement, but call themselves Christian because they try to follow Jesus’ teachings. Maybe there were early Christians who agreed with them, and maybe the author of Q was one of them. If so, the view lost out, and the document was buried. In part, it was buried in the later Gospels of Matthew and Luke, which transformed and thereby negated Q’s message by incorporating it into an account of Jesus’ death and resurrection. One more form of Christianity lost to view until rediscovered in modern times. 
The discovery of Gospel of Thomas was an epiphany in the sense also that it shifted the emphasis from death and resurrection of Jesus Christ. It resurrected a concept of salvation in early Christianity based on correct interpretation and understanding of Jesus’ sayings and the message that was revealed to him, what the Holy Quran calls ‘Injil.’
Some of the following material is fromWikipedia, the free encyclopedia — My additions and highlights are in red color:
Q documentorQ(from the GermanQuelle, “source”) is a postulated lost textual source for the Gospel of Matthew and Gospel of Luke . It is a theoretical collection of Jesus ‘ sayings, written in Koine Greek. Although many scholars believe that “Q” was a real document, no actual document or fragment has been found.
The Two-Source Hypothesis (or 2SH) is an explanation for the synoptic problem, the pattern of similarities and differences between the three Gospels of Matthew, Mark, and Luke. It posits that the Gospel of Matthew and the Gospel of Luke were based on the Gospel of Mark and a lost, hypothetical sayings collection called Q.
The 2SH emerged in the 19th century. Its strengths are its explanatory power regarding the shared and non-shared material in the three gospels; its weaknesses lie in the exceptions to those patterns, and in the hypothetical nature of its proposed collection of Jesus-sayings. Later scholars have advanced numerous elaborations and variations on the basic hypothesis, and even completely alternative hypotheses. Nevertheless, “the 2SH commands the support of most biblical critics from all continents and denominations. 
Synoptic Gospels are Mark, Mathew and Luke:
The following diagram breaks down the details:
1 Introduction2 Synoptic Gospels3 Synoptic problem4 Markan priority and the Triple Tradition5 Two-source hypothesis and the double tradition6 Nature of the Q Document7 Sayings gospels and the Gospel of Thomas7.1 Papias’ mention of a Q-like sayings gospel7.2 Case for a common second source7.3 Case against a common second source8 History of the Q hypothesis 9 Notable contents of Q 10 See also 11 References 12 External links
Nineteenth century New Testament scholars who rejected the traditional perspective of the priority of Matthew in favor of Marcan priority speculated that the authors of Matthew and Luke drew the material they have in common with the Gospel of Markfrom that Gospel. Matthew and Luke, however, also share large sections of text which are not found in Mark. They suggested that neither Gospel drew upon the other, but upon
secondcommon source, termed the Q document. This hypothetical lost text—also called theQ Gospel, theSayings Gospel Q, theSecret of Q, theSynoptic Sayings Source, theQ Manuscript, and (in the 19th century) The Logia—is said to have comprised a collection of Jesus ‘ sayings. Acceptance of the theories of the existence of “Q” and the priority of Mark are the two key elements in the ” two-source hypothesis “. (See also the Gospel of the Hebrews and Streeter ). The two-source hypothesis is the most widely accepted solution to the Synoptic Problem , which concerns the literary relationships between and among the first three canonical gospels (the Gospels of Mark, Matthew, and Luke), known as the Synoptic Gospels. Similarity in word choices and event placement shows an interrelationship. Theories which address the synoptic problem propose how this interrelation came to pass, as well as the nature of this interrelationship. According to the two-source hypothesis, Matthew and Luke both used the Gospel of Mark, independently of one another. This necessitates the existence of a hypotheticalthirdsource in order to explain thedouble traditionmaterial where there is agreement between Matthew and Luke that is not in Mark. This hypothetical source is namedQout of convenience. It has been suggested by many other scholars, however, that if Luke used Matthew’s Gospel as one of his sources (Luke 1:1-3), that there is no need to fabricate yet another source for the material found in common between Matthew and Luke.
Of the many gospels written in antiquity, only four gospels came to be accepted as part of the New Testament: the gospels of Mark, Matthew, Luke, and John. The gospels of Mark, Matthew, and Luke are very similar to one another. These gospels often recount the same stories about Jesus, generally follow the same sequence, and use similar wording.
In contrast, it has long been recognized that the Gospel of John differs significantly from the other three canonical gospels in theme, content, time duration, order of events, and style. Clement of Alexandriafamously summarized the unique character of the Gospel of John by stating
“John last of all, conscious that the ‘bodily’ facts had been set forth in those [earlier] Gospels … composed a ‘spiritual’ Gospel.”
“Synoptic” is a Greek word meaning “one glimpse” or “one look”, referring to the idea that the events seem to have been seen with one pair of eyes (hence the similarities between the gospels). In light of the many commonalities between the gospels of Mark, Matthew, and Luke, these three works are known as the ” Synoptic Gospels “.
The synoptic gospels feature an enormous number of parallels between them. About 80% of the verses in Mark have parallels in both Matthew and Luke. Since this material is common to all three gospels, it is known as the
Triple Tradition. The Triple Tradition is largely narrative but contains some “sayings material”.
Additionally, a substantial block of material is found in both Matthew and Luke (but absent from Mark). About 25% of the verses in Matthew have parallels in Luke (but not in Mark). This material which is common to Matthew and Luke is known as the
Why did Q disappear
Scholars note that the similarities between Mark, Matthew, and Luke are too great to be accounted for by mere coincidence.  Because multiple eyewitnesses reporting the same events never relate a story using identical words, scholars and theologians have long assumed that there was some relationship between the three synoptic gospels that was based upon common literary sources.
The precise nature of the relationships between the gospels of Mark, Matthew, and Luke is known as the
Synoptic Problem. The recognition of the question, and attempts to resolve it, date to antiquity. For example, Augustine of Hippo tried to explain the relationships between the synoptic gospels by proposing that perhaps Matthew was written first, then Mark was written using Matthew as a source, and finally Luke was written using Matthew and Mark as sources. Although this specific solution has fallen out of favor among modern scholars, it represents one of the earliest and most influential proposed solutions to the synoptic problem.
Markan priority and the Triple Tradition
Markan priority hypothesizes Mark was used as a source for Matthew and Luke.
Main article: Markan priority
One of the first steps towards the solution of the synoptic problem was to note that Mark appeared to be the earliest of the four canonical gospels.
Several lines of evidence suggest that this is so. Mark is the shortest of the gospels—suggesting that the longer gospels took Mark as a source and added additional material to it (as opposed to Mark taking longer gospels but deleting substantial chunks of material). Mark’s use of diction and grammar is less sophisticated than that found in Matthew and Luke—suggesting that Matthew and Luke “cleaned up” Mark’s wording (as opposed to Mark intentionally “dumbing down” more sophisticated use of language). Mark regularly included Aramaic quotes (translating them into Greek), whereas Matthew and Luke do not.
For these reasons and others, most scholars accept that the Gospel of Mark was written first, and the Gospels Matthew and Luke use Mark as a source. If Markan priority is correct, the
triple traditionwould be explained as those parts of Mark which both Matthew and Luke chose to copy.
Two-source hypothesis and the double tradition
Main article: Two-source hypothesis
The Gospels of Matthew and Luke were written independently, each using Mark and a second document called “Q” as a source.
Markan priority, while explaining most of the similarities between the three synoptic gospels, is unable to provide a complete solution to the synoptic problem. The Gospels of Matthew and Luke have much material in common. While most of that material appears to have been copied from The Gospel of Mark, some of the material common to Matthew and Luke is not found in Mark.
This material (collectively known as the ”
double tradition“) is often presented in both Matthew and Luke using very similar wording, and often presented in the same order. Since this material is absent from Mark, the use of Mark as a source cannot explain how the same stories, using the same words, came to be found in both Matthew and Luke.
Some scholars therefore suggest that in addition to using Mark as a source, Matthew and Luke may have both had access to some
secondsource, which they both independently used in the creation of their gospels—hence the name “two-source hypothesis”. This hypothetical second source is referred to asQ(from the German “Quelle” meaning “source”).
The two source hypothesis is currently the most widely accepted solution to the synoptic problem.
Nature of the Q Document
If the two-source hypothesis is correct, then the second source, Q, would almost certainly have to be a written document. If Q were merely a shared oral tradition, it could not account for the nearly identical word-for-word similarities between Matthew and Luke when quoting Q material.
Similarly, it is possible to deduce that the Q document, in the form that Matthew and Luke had access to, was written in Greek. If Matthew and Luke were referring to a document that had been written in some other language (for example Aramaic), it is highly unlikely that two independent translations would have exactly the same wording.
The Q document must have been composed prior to the Gospels of both Matthew and Luke. Some scholars even suggest Q may have predated Mark.
The Q document, if it did exist, has since been lost, but scholars believe it can be partially reconstructed by examining elements common to Matthew and Luke (but absent from Mark). This reconstructed Q is notable in that it generally does not describe the events of the life of Jesus: Q does not mention Jesus’ birth, his selection of the 12 disciples, his crucifixion, or the resurrection. Instead, it appears to be a collection of Jesus’ sayings and teachings.
Papias’ mention of a Q-like sayings gospel
Mark having become the interpreter of Peter, wrote down accurately whatsoever he remembered. It was not, however, in exact order that he related the sayings or deeds of Christ. For he neither heard the Lord nor accompanied Him. But afterwards, as I said, he accompanied Peter, who accommodated his instructions to the necessities [of his hearers], but with no intention of giving a regular narrative of the Lord’s sayings. Wherefore Mark made no mistake in thus writing some things as he remembered them. For of one thing he took especial care, not to omit anything he had heard, and not to put anything fictitious into the statements.
While many modern scholars question whether the document which Papias described here is the same document that is modernly known as the Gospel of Mark (see Raymond E. Brown,
An Introduction to the New Testament[New York: Doubleday, 1997], pp. 158ff), this was not the opinion of the the early church nor is it the opinion of many other scholars past and present. The reason for which later scholars doubt whether Papias was referring to the canonical Gospel of Mark is because those who accept its historicity also accept the Markan chronology as a historically correct account of the ministry of Jesus. One of the challenges to denying that Papias was writing about the canonical Gospel is the lack of any historical evidence for two works by Mark, and other statements by church fathers which either parallel or drew from Papias’ statement when speaking of the origin of Mark. It is also possible that, given the universal support for Matthean priority in the early church, Mark’s chronology may have been viewed as “haphazard” where it deviated from Matthew’s.
Papias’ statement, however, poses a significant challenge to the “Q” theory, in that he wrote that Matthew was the
sourcefrom which others drew their Gospel materials, without any mention of Matthew making use of some other document such as “Q”:
Matthew put together the sayings [of the Lord] in the Hebrew language, and each one interpreted them as best he could.
Case for a common second source
The existence of Q follows from the argument that neither Matthew nor Luke is directly dependent on the other in
the double tradition(what New Testament scholars call the material that Matthew and Luke share that does not appear in Mark). However, the verbal agreement between Matthew and Luke is so close in some parts of the double tradition that possibly the most reasonable explanation for this agreement is common dependence on a written source or sources. Even if Matthew and Luke are independent (see Markan priority), the Q hypothesis states that they used a commondocument. Arguments for Q being a written document include:
Sometimes the exactness in wording is striking, for example, Matthew 6:24 = Luke 16:13 (27 and 28 Greek words respectively); Matthew 7:7–8 = Luke 11:9ö10 (24 Greek words each).
There is sometimes commonality in order between the two, for example Sermon on the Plain / Sermon on the Mount .
The presence of doublets, where Matthew and Luke sometimes present two versions of a similar saying but in different contexts. Doublets may be considered a sign of two written sources.
Certain themes, such as the Deuteronomistic view of history, are more prominent in Q than in either Matthew or Luke individually.
Luke mentions that he knows of other written sources of Jesus’ life, and that he has investigated in order to gather the most information. (Luke 1:1–4)
Case against a common second source
Austin Farrer , Michael Goulder ,  and Mark Goodacre have argued against Q, maintaining Markan priority, claiming the use of Matthew by Luke. Other scholars argue against Q because they hold to Matthean priority (see: Augustinian hypothesis ). Their arguments include:
There is a ” prima facie case” that two documents, both correcting Mark’s language, adding birth narratives and a resurrection epilogue, and adding a large amount of “sayings material” are likely to resemble each other, rather than to have such similar scope by coincidence.
Specifically, there are 347 instances (by Neirynck’s count) where one or more words are added to the Markan text in both Matthew and Luke; these are called the “minor agreements” against Mark. Some 198 instances involve one word, 82 involve two words, 35 three, 16 four, and 16 instances involve five or more words in the extant texts of Matthew and Luke as compared to Markan passages.
While supporters say that the discovery of the Gospel of Thomas supports the concept of a “sayings gospel,” Mark Goodacre points out that Q has a narrative structure as reconstructed and is not simply a list of sayings.
Some make an argument based on the fact that there is no extant copy of Q and that no early church writer makes an unambiguous reference to a Q document.
Scholars such as William Farmer maintain that Matthew was the first Gospel, Luke the second, and that Mark abbreviated Matthew and Luke (the Griesbach hypothesis ). Q, part of the Two-Source Hypothesis , would not have existed if Matthean priority is true, as Luke would have got his triple tradition (“Markan”) and double tradition (“Q”) material from Matthew.
Scholars such as John Wenham hold to the Augustinian hypothesis that Matthew was the first Gospel, Mark the second, and Luke the third, and object on similar grounds to those who hold to the Griesbach hypothesis. They enjoy the support of church tradition on this point.
In addition, Eta Linnemann rejects the Q document hypothesis and denies the existence of a Synoptic problem at all. Nicholas Perrin has argued that the Gospel of Thomas was based on Tatian ‘s Gospel and harmony with the Diatessaron instead of the Q document. 
History of the Q hypothesis
If Q ever existed, it must have disappeared very early, since no copies of it have been recovered and no definitive notices of it have been recorded in antiquity (but see the discussion of the Papias testimony below).
In modern times, the first person [ citation needed ] to hypothesize a Q-like source was an Englishman, Herbert Marsh, in 1801 in a complicated solution to the synoptic problem that his contemporaries ignored. Marsh labeled this source with the Hebrew letter
circa125: “Matthew compiled the oracles ( Greek : logia) of the Lord in a Hebrew manner of speech”. Rather than the traditional interpretation that Papias was referring to the writing of Matthew in Hebrew, Schleiermacher believed that Papias was actually giving witness to a sayings collection that was available to the Evangelists.
In 1838 another German, Christian Hermann Weisse , took Schleiermacher’s suggestion of a sayings source and combined it with the idea of Markan priorityto formulate what is now called the Two-Source Hypothesis, in which both Matthew and Luke used Mark
andthe sayings source. Heinrich Julius Holtzmannendorsed this approach in an influential treatment of the synoptic problem in 1863, and the Two-Source Hypothesis has maintained its dominance ever since.
At this time, Q was usually called the
Logiaon account of the Papias statement, and Holtzmann gave it the symbol Lambda (Λ). Toward the end of the 19th century, however, doubts began to grow on the propriety of anchoring the existence of the collection of sayings in the testimony of Papias, so a neutral symbol Q (which was devised by Johannes Weiss based on the GermanQuelle, meaningsource) was adopted to remain neutrally independent of the collection of sayings and its connection to Papias.
In the first two decades of the 20th century, more than a dozen reconstructions of Q were made. However, these reconstructions differed so much from each other that not a single verse of Matthew was present in all of them. As a result, interest in Q subsided and it was neglected for many decades.
This state of affairs changed in the 1960s after translations of a newly discovered and analogous sayings collection, the
Gospel of Thomas, became available. James M. Robinson and Helmut Koester proposed that collections of sayings such as Q and Thomas represented the earliest Christian materials at an early point in a trajectory that eventually resulted in the canonical gospels.
This burst of interest led to increasingly more sophisticated literary and redactional reconstructions of Q, notably the work of John S. Kloppenborg . Kloppenborg, by analyzing certain literary phenomena, argued that Q was composed in three stages. The earliest stage was a collection of wisdom sayings involving such issues as poverty and discipleship. Then this collection was expanded by including a layer of judgmental sayings directed against “this generation”. The final stage included the Temptation of Jesus.
Although Kloppenborg cautioned against assuming that the composition history of Q is the same as the history of the Jesus tradition (i.e. that the oldest layer of Q is necessarily the oldest and pure-layer Jesus tradition), some recent seekers of the Historical Jesus , including the members of the Jesus Seminar , have done just that. Basing their reconstructions primarily on the Gospel of Thomas and the oldest layer of Q, they propose that Jesus functioned as a wisdom sage , rather than a Jewish rabbi , though not all members affirm the two-source hypothesis. Kloppenborg, it should be noted, is now a fellow of the Jesus Seminar himself.
Skeptical of Kloppenborg’s tripartite division of Q, Bruce Griffin writes:
This division of Q has received extensive support from some scholars specializing in Q. But it has received serious criticism from others, and outside the circle of Q specialists it has frequently been seen as evidence that some Q specialists have lost touch with essential scholarly rigor. The idea that we can reconstruct the history of a text which does not exist, and that must itself be reconstructed from Matthew and Luke, comes across as something other than cautious scholarship. But the most serious objection to the proposed revisions of Q is that any attempt to trace the history of revisions of Q undermines the credibility of the whole Q hypothesis itself. For despite the fact that we can identify numerous sayings that Matthew and Luke have in common, we cannot prove that these sayings come from a single unified source; Q may be nothing but a convenient term for a variety of sources shared by Matthew and Luke. Therefore any evidence of revision of Q counts as evidence for disunity in Q, and hence for a variety of sources used by Matthew and Luke. Conversely, any evidence for unity in Q—which must be established in order to see Q as a single document—counts as evidence against the proposed revisions. In order to hold to a threefold revision of Q, one must pull off an intellectual tight-rope act: one must imagine both that there is enough unity to establish a single document and that there is enough disunity to establish revisions. In the absence of any independent attestation of Q, it is an illusion to believe that scholars can walk this tightrope without falling off.
However, scholars supporting the hypothesis of the three-stage historical development of Q, such as Burton L. Mack , argue that the unity of Q comes not only from its being shared by Matthew and Luke, but also because, in the layers of Q as reconstructed, the later layers build upon and presuppose the earlier ones, whereas the reverse is not the case. So evidence that Q has been revised is not evidence for disunity in Q, since the hypothesised revisions depend upon asymmetric logical connections between what are posited to be the later and earlier layers. 
Notable contents of Q
Some of the most notable portions of the New Testament are believed to have originated in Q: 
^ Honoré, A. M. “A Statistical Study of the Synoptic Problem.” Novum Testamentum 10 Aug.-July (1968): 95–147. On page 96 Honoré compares the similarities between the three Gospels with the number of words in common.
^ Matt 3:7–10 & Luke 3:7–9. Text from 1894 Scrivener New Testament
^ Austin M. Farrer, “On Dispensing with Q” in D. E. Nineham (ed.), Studies in the Gospels: Essays in Memory of R. H. Lightfoot (Oxford: Blackwell, 1955), pp. 55–88, reproduced at http://NTGateway.com/Q/Farrer.htm .
^ See, for example, Mark Goodacre, The Case Against Q: Studies in Marcan Priority and the Synoptic Problem (Harrisburg, PA: Trinity Press International, 2002)
^http://www.biblicalstudies.org.uk/pdf/q_linnemann.pdf^ Thomas and Tatian: The Relationship Between the Gospel of Thomas and the Diatessaron by Nicholas Perrin published by the Academia Biblican Society of Biblical Literature 2001 ISBN 1589830458 see also NT Wright on Trusting the Gospels^The Lost Gospel: The Book Q and Christian OriginsMacmillan Co. (1993, paperback 1994).^Reconstruction of Q by Tabor
Text and on-line resources for the Lost Sayings Gospel QThe New Testament Gateway: The Synoptic Problem and QThe Case Against Q, by Mark Goodacre“Jesu Logia (“Sayings of Jesus”)” . Catholic Encyclopedia . New York: Robert Appleton Company. 1913. http://en.wikisource.org/wiki/Catholic_Encyclopedia_(1913)/Jesu_Logia_(%22Sayings_of_Jesus%22) .