Belief in God’s revealed Books
It is a matter of Islamic belief that God, in His mercy, has sent a prophet after another to lead people forth from darkness to light. The belief in all of God’s revealed books is an integral part of Islamic faith.
The Books Mentioned in the Qur'an
There are four Holy books mentioned in the Holy Qur'an:
1- The Sahifa, scrolls given to Abraham;
2- The Torah, the revelations made to Moses;
3- The psalms (Zabor), the psalms given to David;
4- The Gospel (Injil), the teachings given to Jesus.
It is a belief of a Muslim that each of these books (and other books sent by God to His Prophets) was originally a complete revelation. However, for various reasons, most of these revealed books sent by God could not be preserved. For instance, the Quran mentions the scriptures given to Abraham (87:14-19) as Sahifa, but these are no longer in existence and were lost completely. Others were changed in various ways by human intervention.
Thus these previous scriptures are no longer in their original form. They could best be described as edited versions of divine revelations, which have been altered from time to time by editors and commentators. So we can say that those ancient scriptures, which still exist today, have not been preserved from human interpolations.
They have been tampered with at will by their adherents, who have retained the portions they wanted to and deleted the portions they disliked. Therefore, these scriptures have lost their veracity.
The Qur'an, the last book of the divine books, is the only revealed scripture which has been preserved from human interpolation.
The Qur'an enshrines these teachings, which were basically the same as were to be found in previous revealed scriptures. But these scriptures are no longer preserved in their original state. The Qur'an has been preserved in its original state; therefore, it is an eternal guidebook which will never lose its relevance. God has said:
(Indeed, We have sent down the Qur'an, and surely We will guard it from corruption) (Qur'an, 15:9)
By Fatma Dawod
References:
http://www.cpsglobal.org/content/fourth-article-faith-%E2%80%93-belief-revealed-books-kutub
http://www.angelfire.com/ns/perkim/holybook.html
http://www.islam-guide.com/ch3-2.htm