Hadith means “account, “report,” or “narrative,” and consists of mostly oral traditions of the life of the Prophet Muhammad and of early Islam that were passed down for more than 100 years after Muhammad’s death in 632 CE.

The Hadith, mostly consisting of oral traditions in circulation, were not composed during or even shortly after Muhammad’s life and death. In fact, their development was slow and gradual, and they came to include numerous words and actions attributed to Muhammad that have no precedent in the Quran. The Hadith are also considered important not only for a contextual understanding of the Qur’an but also for religious law and moral guidance. Most of Islamic law comes from the Hadith (rather than from the Qur’an) and it is also from the Hadith that the Sunnah, Muhammad’s embodiment of the Qur’anic message, is derived. The contents of the Hadith are encyclopedic covering a vast range of social, commercial, practical, personal, and public matters. These include agriculture, marriage, divorce, Zakat, pilgrimage, festivals, slaves, fasting, diet, funerals, sacrifice, jihad, prayer, faith, recitations of the Qur’an, and much more. There are also theological themes and doctrines ranging from descriptions of the Day of Judgment to Paradise, hell, and creation, as well as the themes of forgiveness, repentance, and so on. It was only in the eighth and ninth centuries CE when Muslims began collecting and compiling the Hadith into a corpus of literature. Although the majority of contemporary practicing Muslims hold to a strong belief in the contents of the Hadith, most still view them as secondary to the Qur’an. A small minority, known as the Quranists, reject the authority of the Hadith collections altogether.

Muslim scholars noticed problems in the Hadith traditions, such as the inclusions of supposed yet dubious traditions of Muhammad, and took to categorizing them into four groups differing in level of authenticity: the Sahih (“authentic”), Hasan (“good”), Da’if (“weak”), or Mawdu’ (fabricated).

Sahih, or authentic, Hadith must have continuity in the chain of transmission that goes straight back to Muhammad himself. It must also be free from contradiction with other established Hadith and it must have been conveyed by a credible person, such as a witness, who memorized and preserved what he heard. A credible person is one who is deemed trustworthy in his religion, understands what he narrates, and can report the wording of the Hadith verbatim. Taken to be the most trustworthy of all the Hadith literature is Sahih al-Bukhari (810-870 CE). Apparently, al-Bukhari’s Sahih took many years to compile having gone through 600 000 memorized items and traditions on which he produced 97 books. Also held in high regard is Sahih Muslim ibn al-Hajjaj (817–875 CE). ibn al-Hajjaj is thought to have sifted through 300 000 traditions to produce his account taking up 57 books. There are also other Sahih Hadith including Sahih ibn Khuzaymah, Sahih ibn Hibban, and Al-Mustadrak alaa al-Sahihain. Ḥasan, or good, Hadith are considered less credible than Sahih but they can stand in as supporting evidence for the Sahih. The narrator of Hasan is considered truthful and reliable but is also deemed less reliable in terms of his memory of Hadith. To be a Hasan, a Hadith must also be free of irregularities. Da’if Hadith fails to obtain the status of Hasan and are considered weak because of doubts around their narrators and because of discontinuity in the chain of transmission. Doubt may be in respect to him being judged as deceitful, prone to making mistakes, and in opposition to the narration of more reliable sources. Mawdu’ are considered fabrications and/or forgeries. These traditions contradict details in the more reliable Hadith and its narrators are known to be liars. Some of these include Kitab al-Abatil by al-Jauraqany and Al-Mawduʻat by Ali al-Qari. These fabrications could sometimes be the work of a heretic.