“And whatever the Messenger gives you, take it, and whatever he forbids you, leave it. And fear Allah: truly Allah is severe in punishment. ” [Holy Quran 59:7]
In Islam, the Arabic word sunnah has come to denote the way Prophet Muhammad (saas), the Messenger of Allah, lived his life. The Sunnah is the second source of Islamic jurisprudence, the first being the Qur’an. Both sources are indispensable; one cannot practice Islam without consulting both of them. The Arabic word hadith (pl. ahadith) is very similar to Sunnah, but not identical. A hadith is a narration about the life of the Prophet (saas) or what he approved – as opposed to his life itself, which is the Sunnah as already mentioned.
In M. M. Azami’s Studies in Hadith Methodology and Literature, the following precise definition of a hadith is given,
“According to Muhaddithiin [scholars of hadith -ed.] it stands for ‘what was transmitted on the authority of the Prophet, his deeds, sayings, tacit approval, or description of his sifaat (features) meaning his physical appearance. However, physical appearance of the Prophet is not included in the definition used by the jurists.’
Thus hadith literature means the literature which consists of the narrations of the life of the Prophet and the things approved by him. However, the term was used sometimes in much broader sense to cover the narrations about the Companions [of the Prophet -ed.] and Successors [to the Companions -ed.] as well. “
The explosion of Islam in the 7th and 8th centuries confronted Islamic scholars with a daunting task: to preserve the knowledge of the Sunnah of the Prophet (saas).From: whyislam.org