Musannaf Ibn Abi Shayba 1:695

Abu Bakr narrated to us, he said: Abu al-Ahwas narrated to us, from Abu Ishaq, from Sulayman ibn Surad, from Jubayr ibn Mut'im, who said: They disputed regarding the ghusl (ritual bath) in the presence of the Messenger of Allah, peace and blessings of Allah be upon him. Some of the people said: "As for me, I wash my head like this and like that." The Prophet, peace and blessings of Allah be upon him, said: "As for me, I pour three handfuls of water over my head."