Some Muslims believe that Christians have corrupted the Bible, whereas their book, the Qur'an, upholds the same Bible, treating it as the the word of God.
God Caused them to Descend (or revealed them)
In the Qur’an, the following terms are used with reference to parts of the Bible:-
- Tawrat – Torah, the first five books of the Bible
- Zabur – the Psalms
- Injil – the Gospel
- Saha'if – the books of the prophets
The Tawrat, the Zabur and the Sahaif are known as the Holy Scriptures of the Jews. Christians call them the Old Testament. The Injil, referred to as the the Holy Scripture of the Christians, is known to Christians as the New Testament. The Qur’an states that all these Scriptures were revealed by God: ‘... confirming that which was (revealed) before it, even as He revealed the Torah and the Gospel’ .
A Guidance for Mankind
The Qur’an emphasises that the Tawrat, the Zabur, the Sahaif and the Injil are God’s books, His word, light, and “Furqan”, which means a criterion for judgement.
- Tawrat - Torah:
- is the book of God 
- is a guidance and reminder for men of understanding 
- Is light and guidance 
- Is “the Criterion”
- “has clear proofs”
- was “... bestowed on him (Isa/Jesus)”.
- has “... guidance and light”.
- is “... confirming . . . the Torah” 
The Qur’an insists that the Injil and the Tawrat are guidance for all mankind, “clear testimonies for mankind, and a guidance and a mercy”.
Injil as a Standard
According to the Qur'an, Christians are told to judge according to the Injil, “Let the people of the Gospel judge by that which Allah hath revealed therein. Whoso judgeth not by that which Allah hath revealed, such are evil livers.” 
Had Muhammad known of any reason to believe that the Injil was not authentic, would the Qur'an have commanded Christians to judge by it? Yet nowadays, some Muslims allege that the Holy Gospel, Injil has been grossly distorted. Either the Muslims who cast doubt on the veracity of the Bible are wrong or Muhammad was severely mistaken.
God’s Word never Changes
The Qur’an claims that no one can alter the word of God. It says, “It is the law of Allah which hath taken course aforetime. Thou wilt not find for the law of Allah aught of power to change.”  In another place, the Qur’an says, “There is no changing the word of Allah – that is the Supreme Triumph.” 
The Qur’an as a Guardian
The Qur’an not only claims to confirm the previous Scriptures but also claims the responsibility of being, “the watcher over it”. Al-Baidhawi (d. 1300) explains that “watcher over it” means, “The Qur’an is the protector of all the sacred books to preserve them from any kind of change”.
The Qur’an does not suggest “alteration”
In the Qur’an the word “tahrif” is never used to suggest that the Biblical text had been altered or corrupted. The word “tahrif”is occasionally used to accuses Jews (but not Christians) of concealing the truth, but in no way to imply that the text had been corrupted.
Different Kinds of “Tahrif”
In the Qur’an, the word “tahrif” is used with the following meanings:-
- To mispronounce words. For example, the Qur’an accuses certain Jews of deliberately distorting Muhammad's words to pervert their meaning: “Some of those who are Jews change words from their context ... distorting (yal'ona) with their tongues and slandering religion.”
- To misinterpret verses. For example, some according to the Qur'an “... used to listen to the Word of Allah then used to change it (tahrif), after they had understood it, knowingly.”
Accusations by Muslim apologists that the text of the Injil and the Tawrat had been corrupted did not arise until long after the Prophet Muhammad. Accusations that the Scriptures had been tampered with first appeared in their writings during the 12th century. 
Before the Prophet of Islam
Some claim that the Injil and the Tawrat were corrupted before the coming of the Prophet of Islam came. If that were so, why does the Qur’an affirm that the message revealed to the Prophet Muhammad was simply a confirmation of the previous Scriptures?
According to the Qur’an, written approximately seven hundred years after the writing of the Injil; the Tawrat and the Injil were in pure form in the Prophet Muhammad’s time. Had the Injil not been genuine and totally accurate at this time, the Qur’an would not have instructed Christians to judge by that which God had revealed in the Gospel.
After the Prophet of Islam
Others charge that the Tawrat and the Injil were changed some time after Muhammad began preaching. However, this charge contradicts the Qur’an, since it claims to be the guardian of the previous inspired books. Thus, anyone who claims that there has been a corruption of the text of the Tawrat or of the Injil also, inevitably, charges the Qur’an with failure in its role as Guardian!
If the pre-Islamic Scriptures had been corrupted, why does the Qur’an order Muslims to believe them? For it bids them to:-
“Say (O Muslims): ‘We believe in Allah and that which is revealed unto us and which was revealed unto Abraham, and Ishmael, and Isaac and Jacob, and the tribes and that which Moses and Jesus received, and that which the prophets received from their Lord. We make no distinctions between any of them, and unto Him we have surrendered”.
Numerous manuscript copies of all parts of the Bible, written centuries before the time of Muhammad, are available today. For example, the Dead Sea Scrolls, which were written before 68 A.D. contain every book of the Old Testament, except the book of Esther. Some of the oldest Greek manuscripts of the entire New Testament, found in Codex form, are also accessible. Two such examples are the Codex Alexandrinus and the Codex Sinaiticus. These manuscripts date from the fourth and fifth centuries A.D. and may be studied in the British Museum in London. Another early manuscript from the same era is the Codex Vaticanus, found in the Vatican Library. There are in various libraries manuscript portions of the New Testament which date back to the second century. The reliability of the present-day Bible may be verified by comparison with such documents.
The modern translations are basically the same in content as those present in Muhammad’s time. They do not differ in any key belief or doctrine. God has preserved his Word in the past and is able to preserve it in the future.
The Bible is changed – Really?
If the Bible and the Qur’an do disagree, they cannot both be right. Has, then, the Qur’an made a mistake in vindicating the Bible? No! For reference has been made to the historical documents which confirm the Bible.
We urge Muslims to follow the Qur’an’s clear advice to Muhammad and his followers: “If thou art in doubt concerning that which We reveal unto thee, then question those who read the Scripture (that was) before thee.” 
Why? Because it is truly, “... a guidance to all mankind”. 
Note: This subject is dealt with in further detail in Dr. Steven Masood's book, 'The Bible and the Qur'an: A question of integrity' (247 pages) available here.
- Qur’an 3:3
- Qur’an 2: 101, 3:23, 5:44
- Qur’an 40:53-54
- Qur’an 5:44
- Qur’an 2:53, 21:48
- Qur’an 2:87
- Qur’an 5:46
- Qur’an 28:43, cf. 3: 3-4, 6:92
- Qur’an 5: 47
- Qur’an 48: 23
- Qur’an 10: 64, 6: 34.
- Qur’an 5: 48
- Qazi Nasiruddin Abusaeed Abdullah bin Umar al-Baidhawi (1300 AD) wrote a well-known commentary on the Qur’an, originally called “Anwar-al-tunzeel”, but now known as “Tafsir-e-Baidhawi”.
- Qur’an 4: 46, cf. 3: 78. The Imam Fakr al Din Al Razi (d. 1228) believed that the “tahrif” referred to in the Qur’an was in meaning, not in text. He wrote the voluminous commentary on the Qur’an which is properly known by many Muslims as “The Great Tafsir”.
- Qur’an 2: 75. In his book “Alfouz al kabeer fi Osulal tafsir” Shah Waliullah states that in the Qur’an “tahrif” refers to the Jews misquoting or mistranslating the Torah and he asserts that the original was not and cannot be altered, it being the word of God.
- Colin Chapman, “You Go and do the Same” (CMS: London 1983). p. 53.
- Qur’an 2: 136
- Qur’an 10: 94
- Qur’an 3: 4