Musnad Ahmad 30:300

Yahya narrated to us, from Ibn ‘Ajlan, from Sa‘id, from Abu Hurayrah, that a man said: "How much is sufficient for my head in the ritual bath (ghusl) from major ritual impurity (janabah)?" He said: "The Messenger of Allah (peace and blessings of Allah be upon him) used to pour [water] with his hand over his head three times." He said: "But my hair is thick." He said: "The hair of the Messenger of Allah (peace and blessings of Allah be upon him) was thicker and better."