Musnad Ahmad 33:147

Hushaym narrated to us, from Abu Bishr, from Abu Sufyan, from Jabir, that the Prophet, peace and blessings of Allah be upon him, was asked about the *ghusl* (ritual bath) for *janabah* (major ritual impurity). The Prophet, peace and blessings of Allah be upon him, said: "As for me, I pour three [handfuls of water] over my head."