The Qur'an or Koran is the holy book of Islam. According to one Muslim tradition, it was written by God and revealed to Muhammad by the angel Gabriel from his first revelation at forty until his death at sixty-two. In another of the many traditions regarding the writing of the Qur'an, Muhammad had the revelations written down on pieces of paper, stones, palm leaves, or whatever writing materials were available. He indicated to the scribes the context in which the passages should be placed.

After the prophet's death, it was decided to find people who had learned the words by heart and to locate written excerpts from all parts of the Muslim Empire. The resulting information was edited to complete a correct edition of the work. Thus, an authoritative text of the Qur'an was eventually produced. It is held in very high regard; its Arabic language is considered unsurpassed in beauty and purity. To imitate the style of the Qur'an is a sacrilege.

The Qur'an is the primary source of every Muslim's faith and practice. It deals with the subjects that concern all human beings: wisdom, beliefs, worship, and law. However, it focuses on the relationship between God and his creatures. It also provides guidelines for a just society, proper human relationships, and equal division of power. The Qur'an also posits that life is a test and everyone will be rewarded or punished for their actions in the next life. For example, on the last day, when the world comes to an end, the dead will be resurrected and a judgment will be pronounced on every person in accordance with their deeds.

Another source of Islamic doctrine is the Hadith (a report or collection of sayings attributed to the prophet and members of the early Muslim community). The Hadith is second only to the authority of the Qur'an. It is considered the biography of Muhammad created from the long memory of the members of his community. Hadith was a vital element during the first three centuries of Islamic history, and its study gives a broad index into the philosophy of Islam.

To the non-Muslim, the Hadith is an introduction to the world of Islam with almost encyclopedic inclusiveness. Provisions of law are the primary element, dealing with the moral, social, commercial, and personal aspects of life and the theological aspects of death and final destiny. The content of the Hadith has the kind of minutia found in the Talmud, the body of Jewish civil and ceremonial law and legend.

There is evidence of the impact on Islam of Jewish and Christian philosophies and theology, particularly as they relate to the last judgment. Together, the Qur'an and the Hadith form the basis of Islamic law.