Nowhere does Al-Qur'an accuse Christians of changing the written words of the Holy Books of the Jews and the Christians. It only accuses the People of the Book of "taharif" -- changing the meaning with their tongue, and keeping hidden other portions of scripture.
There is among them a section who distort the Book with their tongues:
Surat-u Ali-Imran (3):78
For those who allege that the Scriptures have been altered is the task of providing the true text in order to prove what exactly has been changed. The most common attempt has been the distribution of the "Gospel of Barnabas." However, this attempt has proved embarrassing since it contains many contradictions to Al-Qur'an. Though variant readings exist in the early manuscripts of the Bible, there is nothing to indicate deliberate changes for the sake of tampering with doctrine. The existence of variant readings is also true of Al-Qur'an. Notice the following excerpt taken from page xxxvi of the introduction to THE HOLY QUR'AN by Yusuf Ali, 2nd Edition, 1977.
From the above historical facts, it must have become clear that the reading of the Qur'an (with a few minor variations is the same as practised and taught by the Holy Prophet. the scholars and Qurra** of the Quran have been unanimous in asserting that only that reading will be authentic which (a) conforms to the script of the copy, circulated by Hadrat Uthman and (b) complies with the lexicon of Arabic, its usages, idioms and grammar, and above all, (c) is traceable by genuine and continuous links to the Holy Prophet himself. That is why there are only a few variations in its reading and those are not contradictory in their meaning but enlarge their scope and make them more comprehensive. Thus there is absolutely no doubt that the Holy Prophet himself practised those various readings in the instances which exist today, and they make the meanings more comprehensive.For example, let us take the two authentic readings of (a) verse 3 of Al-Fatihah and (b) verse 6 of Al-Ma'-idah. One reading of I:3, that is, "arabic image" means the "Master of the Day of judgement" and the other reading means, "the Sovereign of the Day of judgement". It is obvious that these two readings make the meaning of the verse all the more clear. (c) One reading of V:6, that is, "arabic image" means "... wash your faces ... and (wash) your feet" as is done at the time of performing ablution with naked feet. The second reading, that is, "arabic image" means "... wash your faces and wipe your heads and (wipe) your feet" with wet hands.
Reproduction from Yusuf Ali's "The Holy Qur'an Translation and Commentary," 2nd Edition, 1977
If such an accusation about the alteration of the Bible is to be considered, then the following questions must be addressed:
Question (1)... Who changed the Scriptures?
It is often alleged that the Jews and Christians jointly altered the Scriptures in order to hold back the spread of Islam. But this is highly unlikely since the Jews and Christians themselves differed widely.
The Jews say "The Christians have naught (to stand) upon;" and the Christians say, "The Jews have naught (to stand) upon." Yet they (profess to) study the (same) book. Surat-ul Baqara (2):113
Had the Scriptures been changed to alter doctrine, surely there would have been some objections, as there existed many sects both within Judaism and Christianity. Church history, however, makes no mention of such accusations. Accusations pertain not to the changing of Scripture, but rather to the false interpreting of Scripture.
Jesus himself never accused the Jews of altering the Scriptures, but instead, drew their attention to them. Had changes been made, Jesus certainly would have exposed them.
The true Christian scholars during the time of Muhammad who befriended the Muslims (such Christians were the Abyssinians) would certainly have exposed any attempted changes in the Scriptures.
Nearest among them in love to the believers will thou find those who say "We are Christians" because amongst these are men devoted to learning.
Surat-ul Maida (5):82
Question (2)... When were the Scriptures supposedly altered?
If the Scriptures of the Jews and Christians were altered before the death of Muhammad, then surely he would not have been instructed by God to recite the following:
I believe in the Book (of the People of the Book) which God has sent down...
Surat-ush Shura (42):15We believe in God, and the revelation given to us, and to Abraham, Ishmael, Isaac, Jacob, and the Tribes, and that given to Moses and Jesus, and that given to (all) Prophets from their Lord. We make no difference between one and another of them.
Surat-ul Baqara (2):136O People of the Book Ye have no ground to stand upon unless ye stand fast by the Law, the Gospel, and all the revelation that has come to you from your Lord.
Surat-ul Maida (5):68Let the People of the Gospel judge by what God has revealed therein.
Surat-ul Maida (5):47And in their footsteps we sent Jesus the son of Mary confirming the Law that had come before him. We sent him the Gospel: therein was guidance and light, and confirmation of the Law.
Surat-ul Maida (5):46If thou (Muhammad) are in doubt as to what We have revealed, then ask the People of the Book.
Surat-u Yunus (10):94And when there comes to them a Book (Qur'an) from God confirming what is with them... ... yet they reject all besides even if it be truth confirming what is with them... And when there came to them an Apostle of God confirming what was with them... Surat-ul Baqara (2):89, 91, 101
Note in the above references as well as others the phrase "confirming what is with them..." These verses are clear in teaching that the Qur'an came to confirm the previous Scriptures; not to correct them or replace them, as many would have us to believe! Nowhere does Al-Qur'an say it came upon man to save him from the corruption, alteration, or disappearance of the previous Holy Books, namely the Tawrat (writings of Moses) and the Injil (New Testament).
It is highly unlikely that the Scriptures could have been altered after the death of Muhammad for the following reasons:
By 600 A.D., Christianity had spread into Asia, Africa, and Europe. There is no evidence of a worldwide council that met for the purpose of altering the Scriptures.
Since Muslims revere the Holy Books, converts from Judaism and Christianity would have retained the true texts; however, such texts are nowhere to be found.
Manuscripts still exist from the fourth and fifth centuries (Muhammad lived in the sixth century). These manuscripts line up with today's translations of the Scriptures and any variant readings are noted.
Question (3)... How was it changed?
Since Judaism and Christianity spread throughout the world, it would have been impossible for anyone to collect all the Holy Books, manuscripts, and writings containing Scriptural references from all churches, synagogues, libraries, schools, and homes, and make the changes, and then return them all without anyone knowing!
Al-Qur'an itself says no one can alter the Word of God:
The Word of thy Lord doth find its fulfillment in truth and in justice. None can change His Words.
Surat-ul An'am (6):15No change can there be in the Words of God.
Surat-u Yunus (10):64
If Muslims claim from these verses that God has been able to protect the Qur'an from any corruption, then it should be possible for them to believe that God is powerful enough to preserve all the previous Holy Books as well!
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