Sahih Muslim Book 30, Hadith Number 5773.

Chapter : Concerning the characteristic features of Allah’s Apostle (may peace be upon him), and he was the most handsome of the people.

Qatada reported: I asked Anas b. Malik: How was the hair of Allah’s Messenger (may peace be upon him)? Thereupon he said: His hair was neither very curly nor very straight, and they hung over his shoulders and earlobes.