Musnad Ahmad 1153:248

Yahya and Waki’ narrated to us, from Hisham, the meaning [of the narration]. Yahya said: My father informed me, saying: Aisha informed me regarding the Messenger of Allah’s (peace and blessings of Allah be upon him) bathing from major ritual impurity (janabah). She said: "He would begin with his hands and wash them." Waki’ said: "He would wash his palms three times. Then he would perform his ablution (wudu) for prayer. Then he would rub the roots of his hair with his fingers until, when he thought he had cleansed the skin, he would scoop three handfuls and pour them over his head, then he would pour [water] over the rest of his body." Ibn Numayr said: "He scooped with his hands, filling his palms three times."