Musannaf Ibn Abi Shayba 1:696

Abu Khalid al-Ahmar narrated to us, from Muhammad ibn ‘Ajlan, from Sa‘id ibn Abi Sa‘id, from Abu Hurayrah, who said: A man asked him, "How much [water] should I pour over my head while I am in a state of janabah (major ritual impurity)?" He said: "The Messenger of Allah (peace and blessings of Allah be upon him) used to pour three handfuls over his head." The man said: "Indeed, my hair is long." He said: "The Messenger of Allah (peace and blessings of Allah be upon him) had more hair than you, and was better."