Waki' bin al-Jarrah وكيع بن الجراح · The Book of Ghusl and Tayammum

"I remember performing Ghusl - myself and the Messenger of Allah (ﷺ), from this" - a vessel like a Sa' or smaller. "We both started taking water from it and I poured water over my head with my hand, three times, without undoing any of my hair."