The Hadith The second most important collection of texts, second only to the Qur'an in terms of theological authority, are the Hadith. The words of the Qur'an are considered to have been revealed to Muhammad. The Hadith are a collection of oral traditions centered around the life of the Prophet which set forth his methodologies of worship, his Qur'anic interpretations, advice, commands, warnings, prophecies, and rules for everyday life. The Hadith are not classified as Revelation, although a small portion known as the 'Sacred Hadith' (Hadith Qudsi) are considered illuminated inspiration (ilhaam); i.e divine exhortations and messages restated in Muhammad's own words.

Islamic science rivaled and even surpassed the sciences of Antiquity. Islamic astronomers developed the Astrolabe, an indispensable instrument for the Muslim traveler. It enabled him to pinpoint the stars and the times of day, so as to honor the time of prayer and to establish the orientation towards Makkah.

The origins of many Hadith texts are unknown. Therefore, a rigorous system of authentication and referencing grew around the process of collecting and tabulating Hadith in written form. There were scores of specialists who dedicated themselves to this task, who traveled far and wide not only to collect oral and written Hadith, but also to verify or authenticate them. One famous scholar sifted through over 300,000 Hadith narratives, and found that only 4,000 could be authenticated. This science of authentication (Asmaa-ul-rijaal) is thought to have given rise to the modern Western academic custom of referencing sources. Generally speaking, each of the individual Hadith narrations is comprised of two parts: the isnad or list of transmitters that indicate the provenance of the document (and thus establishes its chain of narration back to the Prophet or someone who witnessed the Prophet); and the second part is the matn or text and subject proper.

Among the first collection of narrations to be compiled was the Musnad of Ahmed ibn-Hanbal in the early 9th century. It was followed a group of works by numerous editor/authenticators that is collectively referred to as al-Kutub al-Sitta or 'The Six Books.