Musnad Abu Ya'la al-Mawsili 149:126

Ibrahim narrated to us, Hammad narrated to us, from Hisham ibn Urwah, from Urwah, from Aisha, that the Messenger of Allah (peace and blessings of Allah be upon him), when he wanted to perform ghusl (ritual bath) from janabah (major ritual impurity), would perform wudu (ablution) like his wudu for prayer. Then he would insert his hand into the vessel and trace the roots of the hair with his right hand on his right side, and he would take with his left hand and trace the roots of the hair on his left side, until, when he thought he had cleared the entire skin, he would pour [water] over his head. Hisham said: Except that he would begin before that by washing his hands three times each, and he would wash his private parts.