Musnad Abu Ya'la al-Mawsili 108:79

Zuhayr narrated to us, Ibn 'Uyaynah narrated to us, he said: Ja'far heard his father narrating to him from Jabir, that the Prophet (peace and blessings of Allah be upon him) used to pour three scoops [of water] over his head, meaning during the ritual bath (ghusl).