It was narrated from Abu Hurairah that :
A man asked him: "How much water should I pour over my head when I m sexually impure?" He said: "the messenger of Allah used to pour three handfuls of water over his head." The man said: "My hair is long." He said: "The Messenger of Allah had more hair than you and he was cleaner."
English reference: Vol. 1, Book 1, Hadith 578
Arabic reference: Book 1, Hadith 621