Musnad Ahmad 33:315

Yahya narrated to us, from Ja’far, my father narrated to me, he said: Jabir said to me: Your cousin, al-Hasan ibn Muhammad, asked me about the ritual bath for major impurity (janabah). I said: "The Messenger of Allah (peace and blessings of Allah be upon him) used to pour three handfuls over his head." He said: "I have a lot of hair." I said: "Desist, O son of my brother. The hair of the Messenger of Allah (peace and blessings of Allah be upon him) was more than your hair and better."