Prophet Muhammad's sayings and deeds are called sunnah, which are transmitted to us through hadith or oral traditions that recount events in the lives of the Prophet. Those scholars who specialize in this field are known as Muhaddithîn.
There are six major collections of such hadith in Sunni Islam known as Al-Kutub al-Sittah or Sihah Sittah. Sahih is an Arabic word, one of whose meanings is "authentic." Sunan is the plural of the Arabic word “sunnah” meaning “custom.”