Reports on the sayings and the traditions of Prophet Muhammad (s.a.w.) or what he witnessed and approved are called Hadith. These are the real explanation, interpretation, and the living example of the Prophet (s.a.w.) for teachings of the Qur'an. His sayings are found in books called the Hadith books.
Some famous collectors of Hadith are Imam Al-Bukhari, Imam Muslim, Imam An-Nasa'i, Imam Abu Dawood, Imam At-Tirmizi, and Imam Majah. There are many others.