A Ḥadīth (pl. Aḥādīth احاديث) is a traditional report of what the Prophet Muhammad ﷺ did, said or approved of at some point in his life. After the Qurʾān, the second most important source in Islam is the living example set by Muḥammad ﷺ, called the Sunnah. The Aḥādīth also provide essential historical context to the events surrounding the revelation of the Qurʾān.
For generations, biographical accounts of Muḥammad ﷺ were transmitted both in writing and orally as accurately as possible. During the life of After the death of Muḥammad ﷺ, Islām had grown across a wide geographic area, spanning many different cultures. Some groups were in conflict with one another. It was at this time that scholars travelled far and wide to interview Muslims and collect all the narrations that were being preserved orally. These scholars had to be extremely careful in their work. They sceptically analyzed all available reports to determine which ones could be considered accurate, based on a number of criteria, such as the chain of narration, the reputation of the narrators, and so on.
ʿIlm al-Ḥadīth (Ḥadīth studies) is a whole field of study in Islam.