Belief in Scriptures
“Blessed be He Who sent down the criterion (i.e. this Qur'an) to His slave (Muhammad) that he may be a warner to the 'Alamin (mankind and jinn).”  
Qur’an 25:1
Belief in the scriptures revealed by God is the third article of Islamic faith. We can identify four main reasons for the revelation of the scriptures:
1. The scripture revealed to a prophet is a point of
    reference to learn the religion and obligations
    towards God and fellow human beings. God
    reveals Himself and explains the purpose of
    human creation through revealed scriptures.
 
2. By referring to it, disputes and differences
    between its followers in matter of religious belief
    and practice or in matter of social practice could
    be settled.
 
3. The scripture are meant to keep the religion safe
    from corruption and deterioration, at least for
    some time after the death of the prophet.
    At the present time, Qur’an revealed to our 
    Prophet Muhammad (may the mercy and
    blessings of God be upon him) is the only
    scripture to remain safe from corruption.
 
4. It is God’s proof against human beings. They are
    not allowed to oppose or overstep it.
 
Muslims uphold and respect the following scriptures:
1. The Qur’an itself, revealed to the Prophet
    Muhammad (peace be upon him)
 
2. The Torah (Tawrah in Arabic) revealed to the
    Prophet Moses (different from the Old Testament
    read today).
 
3. The Gospel (Injeel in Arabic) revealed to Prophet
    Jesus (different from the New Testament read in
    churches today)
 
4. The Psalms (Zaboor in Arabic) of David.
 
5. The Scrolls (Suhuf in Arabic) of Moses and
    Abraham.
Muslims believe whatever is true in them and has neither been altered or deliberately misconstrued. Islam affirms that God revealed the Qur’an as a witness over the previous scriptures and confirmation of them, because,
 
Allah, the Exalted, says: “And We have sent down to you [O Muhammad] the Book (the Qur’an) in truth, confirming the scripture that came before it and (trustworthy in highness and awitness) over it (the collection of old scriptures) ...” Qur’an 5:48
 
Meaning the Quran confirms whatever is true in previous scriptures and rejects whatever alterations and changes human hands have made to them. The Holy Quran is different from other scriptures in the following respects:
1. The Quran is miraculous and inimitable. Nothing
    similar to it can be produced by human beings.
 
2. After the Quran, no more scriptures will be
    revealed by God. Just as the Prophet Muhammad
    (Peace Be Upon Him) is the last prophet, the
    Quran is the last scripture.
 
3. God has taken it upon Himself to protect the
    Quran from alteration, to safeguard it from
    corruption. On the other hand, previous scriptures
    suffered alteration and distortion and do not
    remain in their originally revealed form.
 
4. The Quran, for one, confirms early scriptures and,
    for another, is a trustworthy witness over them.
 
5. The Ouran abrogates them, meaning it cancels
    the rulings of the previous scriptures and renders
    them inapplicable. the Law of the old scriptures
    is no longer applicable; the previous rullings have
    been abrogated with the Law of Islam.
(This is) a book which We have revealed unto you (O Muhammad) in order that you might lead mankind out of darkness (of disbelief and polytheism) into light (of belief in the Oneness of Allah and Islamic Monotheism) by their Lord's Leave to the Path of the All-Mighty, the Owner of all Praise.   Qur'an  14:1