Sayyidah Aishah (may Allah be pleased with her) says: When the Messenger of Allah (peace and blessings be upon him) took a ritual bath, he would first pour water over his right hand and wash it; then with his right hand he would pour water over the impurity that was on him and wash it off with his left hand, until, when he (peace and blessings be upon him) had finished with that. I think (the narrator) added these words: he would pour water over his head.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 814