The vast body of reported words, deeds, and silent approvals of the Prophet Muhammad — transmitted through chains of named witnesses, sifted by an elaborate science of authentication, and gathered into canonical collections — that stands after the Quran as the second source of Islamic law and practice for mainstream Sunni and Shia Islam, though the accepted collections differ.
How do you pray five times a day when the book that commands it barely says how? The Quran commands prayer and marks its times, but it does not lay out the full ritual form: the postures, the units, the words. For that, and for a thousand other questions of daily life, Muslims turned to the example of the Prophet — remembered, repeated, and written down as short reports called hadith. Each report arrives with a credential attached: a chain of names tracing it back, witness by witness, to the man who said it. Over centuries, scholars built one of the most demanding systems any premodern culture devised for deciding which of those chains to trust.