'an anthology of the sayings of the prophet Muhammad'
There are two main sources for an understaning of Islam: the Holy Qur'an and teh collections of the recorded words, actions and sanctions of the Prophet Muhammad which make up the sunna and which are normally referred to as Hadith.
As the Holy Qur'an is the word of Allah it must be strictly followed; in the same way the teachings contained in the Prophet's sunna must be observed by all who profess to be Muslims, for about them the Holy Qur'an says: "And whatsoever the Messenger giveth you, take it. And whatsoever he forbiddeth, abstain (from it)."
Thus the sunna, in the form of Hadith, is complementary to the Holy Book itself: it helps to explain and clarify the Holy Qur'an and to present practical applications of its teachings. Without a study of Hadith a Muslim's knowledge of his faith remains incomplete, and without it the non-Muslim is unable to form a true picture of Islamic faith and its fundamental spiritual, moral, legislative, and cultural principles.