First of all, it should be clear that believing in the previous Divine Books is one of the articles of faith. In the Qur’an Allah says, “The Messenger believeth in that which hath been revealed unto him from his Lord and (so do) the believers. Each one believeth in Allah and His angels and His scriptures and His messengers. We make no distinction between any of His messengers and they say: We hear, and we obey. (Grant us) Thy forgiveness, our Lord. Unto Thee is the journeying.” (Al-Baqarah: 285). Also, the Prophet (peace and blessings be upon him) disclosed that iman necessitates belief in the previous Divine Books when he said: “Iman is to believe in Allah, His Angels, His Books, His Messengers, and the Last Day, and to believe in Divine destiny, both the good and the evil thereof.” However, belief in the fact that Allah sent Books prior to the Qur’an does not imply that the extant books of the other religions are not corrupted. We Muslims believe in what was originally revealed to the prophets before Muhammad (peace be upon them all), not in what remains of those revelations.
The prominent Muslim scholar Dr. Muhammad Abu Laylah, professor of the Islamic Studies and Comparative Religions at Al-Azhar University states: “Muslims believe that Islam is the religion of Allah that came to mankind with all prophets of Allah from Adam to Muhammad at different times. Each came according to the level of people and according to the circumstances of his time. So, Adam, Noah, Abraham, Jesus and finally Muhammad (peace and blessings be upon them all) brought essentially the same religion. No prophet ever taught anything of his own or ever contradicted another prophet.
Thus, Muslims believe in all prophets and in the revelation that they brought from Allah without distinction or discrimination between one prophet and the other.
Referring to this, Allah Almighty says: “He hath ordained for you that religion which He commended unto Noah, and that which We inspire in thee (Muhammad), and that which We commended unto Abraham and Moses and Jesus, saying: Establish the religion, and be not divided therein. Dreadful for the idolaters is that unto which thou callest them. Allah chooseth for Himself whom He will, and guideth unto Himself him who turneth (toward Him).” (Ash-Shura: 13)
In the Qur’an, Allah tells us also that He gave the kalimat or words of guidance to Adam, the Scroll to Abraham, the Psalms to David, the Torah to Moses, the Gospel to Jesus. And He also tells us that some of these Books are completely lost. Others are subject to corruption and omission. Thus, basically, Muslims believe in all of these Books and of the prophets who brought them.
The essential Divine message, which Allah saved from human intervention, is there in the Qur’an. The Bible, that is to say, the Old and New Testaments, contains some original passages and parts of the teachings of the preceding prophets.
This is the truth about the previous Divine Scriptures, but Islam recommends us not to argue with the People of the Book, i.e. Jews and Christians, unless such argument is done in the best of manners and not to provoke them or to belittle their beliefs.”