Musnad Abu Ya'la al-Mawsili 160:143

And with his chain of narration from Abu Hurayrah, he said: A man asked him, "How much should I pour over my head while I am in a state of major ritual impurity (junub)?" He said: "The Messenger of Allah (ﷺ) used to pour three handfuls over his head." The man said: "My hair is long." He said: "The Messenger of Allah (ﷺ) had more hair than you, and was better."