This was actually my reply to a brother asking how to reply to allegations made against the preservation of the Quran:I think brother the answer is very simple!
First we should not over react to the claims about doubt in the preservation of the Quran, I have seen hundreds of new converts to Islam I never saw one saying that he had problem or difficulty with that before he becomes Muslim or even after he became Muslim!, also I have entertained many Christians who know about the Quran and when I ask them why not to accept the Quran no one say because it is not preserved! Usually they say because it says Jesus pbuh is not the son of God or that Jesus pbuh was not crucified! They reject the Quran because the Quran opposes their tradition!
Now back to the answer, are we talking about the Quran that we have today? Is their any rejection that what we have today is the same canon of Othman! The answer is NO! Both Muslim and non Muslim scholars agree that the Quran that we have today is the one authorized by Othman may Allah be pleased with him and there is no divergent texts like the case in all non Islamic scriptures; so, there is no point in over clarifying this and here is a non Muslim reference reporting the agreement about this point:
Qurʾan , Encyclopedia of the Modern Middle East and North Africa 2004 "Contemporary Orientalist views of the collection of the Qurʾan diverge widely, ranging from the claim that it is a late forgery to near-total endorsement of traditional Muslim claims. However, with very few exceptions, there is general agreement that the current text of the Qurʾan is in accordance with Uthman's canon (as there are no traditions referring to other canons), and that the variations that prompted codification of the Qurʾan were mostly minor divergences of pronunciation and orthography and omissions in some personal copies of some chapters or insertions of prayer formulas external to the text. More importantly, it seems that the early Muslim community accepted the Uthman canon: There were no attempts made by the early dissenting political groups (Shiʿite and Khawarij) to claim a divergent text; instead, they insisted on a divergent interpretation of it."
Second, was there any corruption done by Othman himself? My approach is simple! Is Othman an acceptable authority? The answer is YES, because he was a major companion of the prophet pbuh, next who led the compilation? Zaid ibn Thabit, was he an acceptable authority? The answer is YES, because he was one of the major scribes of the prophet pbuh and he was the same chief scribe who made the compilation in the time of Abu baker may Allah be pleased with him
So, this Quran that we have was compiled by the same major companions and scribes of the prophet pbuh himself! Now was their any significant opposition to the Quran that was compiled by Othman by the other companions? The answer is NO, many of the major companions of the prophet were alive and witnessing this compilation and none of them objected! Even Abdullah ibn Masoud may Allah be pleased with him who resisted giving his personal copy did not object to the new compilation! He did not say this Quran that was compiled by Othman is corrupt! Even the enemies of Othman Alkhawarij did not object to this Quran! All the copies that were ordered by Othman to be burned were personal unauthorized copies parts or complete, example is Zaid ibn Thabit himself had a personal copy of the Quran and he had to give it up!
Is there an additional proof that the Quran is preserved? The answer is YES, the Quran is transmitted to us orally and we have authentic and continuous chain of transmission up to the five major companions of the prophet who were famous in teaching the Quran and one of them is Ali bin Abi Talib and also Abdullah ibn Masoud may Allah be pleased with them, because any authentic reading of the Quran has three conditions: has to be authentic narration to the companions, consistent with a written manuscript and consistent with Arabic language! So, we have oral transmission of the Quran that goes beyond the Quran that was complied by Othman may Allah be pleased with him!
Finally, one has to examine the Quran to see if it is the word of Allah swt, the Quran proves itself to be from Allah swt it can't be imitated and it is perfect without contradictions or mistakes, so if this is the case it must have been preserved!
Now, we tell Christians searching for the truth if you really can produce a gospel authored by any of the true disciples of Jesus pbuh like Matthew we as Muslims are more that willing to accepted it to be the word of God!
Gospel & Gospels, Catholic Encyclopedia "the New Testament differ from its apocalyptic and epistolary literature, as those of the Old Testament differ from its prophecy, in being invariably anonymous… Prophecies whether in the earlier or in the later sense, and letters, to have authority, must be referable to some individual; the greater his name, the better... it thus appears that the present titles of the Gospels are not traceable to the Evangelists themselves."
Introduction of Matthew's Gospel, New American Bible "The ancient tradition that the author was the disciple and apostle of Jesus named Matthew (see Matthew 10:3) is untenable because the gospel is based, in large part, on the Gospel according to Mark (almost all the verses of that gospel have been utilized in this), and it is hardly likely that a companion of Jesus would have followed so extensively an account that came from one who admittedly never had such an association rather than rely on his own memories. The attribution of the gospel to the disciple Matthew may have been due to his having been responsible for some of the traditions found in it, but that is far from certain. "
Biblical source, Encyclopedia Britannica Online "Most of the writings in the Old Testament are of anonymous authorship, and in many cases it is not known whether they were compiled by individuals or by groups"
By Sereihan Alshammari