Muhammad was illiterate. The text he received from Allah and dictated to scribes, compiled and referenced only eighteen years after his death in 632 CE, is called the Qur'an ("Recitation"; also transliterated as Koran). As one of the most recent of the world's scriptural texts, it has a strong historical basis. And because it cannot truthfully be translated from its original Arabic, we know exactly what Muhammad caused to be written, down to the very last word. For those who cannot read Arabic, it has, of course, been translated into various languages. But those translations are not considered to be valid copies of the Qur'an. They are simply aids.
The Qur'an is divided into 114 chapters (suras), which are further divided into a total of some 6,000 verses. In length, it is roughly the same as the Christian New Testament.
Sura 1 immediately places Allah at center stage:
In the name of God, Most gracious, Most Merciful, Praise be to God, The Cherisher and Sustainer of the Worlds: Most Gracious, Most merciful; Master of the Day of Judgment. Thee do we worship, And Thine aid we seek. Show us the straight way, The way of those on whom Thou hast bestowed Thy Grace, Those whose (portion) is not wrath, and who go not astray.
The Qur'an goes on to defines the quintessential monotheistic theological statement:
There is no God but [Allah]; That is the witness of Allah, His angels, and those endued with knowledge, standing firm on justice. There is no God but He, the Exalted in Power, the Wise (3:18)
Muhammad saw both Jews and Christians as people to whom God had spoken in the past. He called them People of the Book:
Mankind was one single nation, and Allah sent Messengers with glad tidings and warnings; and with them he sent the Book in truth, to judge between people in matters wherein they differed; but the People of the Book, after the clear Signs came to them, did not differ among themselves, except through selfish contumacy (2:213) ... Say, "O People of the Book! Come to common terms as between us and you: That we worship none but Allah" (3:64).
Many of the stories of the Jewish scriptures are told as well in the Qur'an:
He it is who created the heavens and the earth is Six Days. (57:4)
We said: O Adam! Dwell thou and they wife in the Garden; and eat of the bountiful things therein. (2:34)
And remember that Abraham was tried by his Lord with certain commands, which he fulfilled: He said, "I will make thee an Imam to the Nations." (2:124)
Behold! The angel said: "O Mary! Allah hath chosen thee and purified thee—chosen thee above the women of all nations." (3:42)
Then will Allah say: "O Jesus the son of Mary! Recount My favour to thee and to thy mother. Behold! I strengthened thee with the holy spirit, so that thou didst speak to the people in childhood and maturity." (5:110)
Many of the stories, of course, differ somewhat from their Jewish or Christian counterparts. Ishmael, Abraham's eldest son, is the one to whom a blessing is imparted, not Isaac, the youngest. Jesus is crucified and dies in the Christian scriptures. But in the Qur'an: "they killed him not, nor crucified him, but so it was made to appear to them, and those who differ therein are full of doubts, with no (certain) knowledge, but only conjecture to follow, for of a surety they killed him not: Nay, Allah raised him up unto himself: And Allah is exalted in power, Wise" (4:157-158).
These common stories probably mean that Muhammad's audience was already familiar with the stories of both the Hebrew and Christian scriptures. But the Qur'an is considered by Muslims to be the final revelation by God to humankind. It completes the divine revelation. It is God's final word until that day when "Allah reward[s] the righteous, (namely) those whose lives the angels take in a state of purity, saying (to them), `Peace be on you; enter ye the garden, because of (the good) which ye did (in the world)'" (16:27-32).