Sunan Abi Dawud 240

Aishah reported :when the Messenger of Allah (May peace be upon him) wanted to wash himself because of sexual defilement, he called for a vessel like HILAB (a vessel used for milking the camel). He then took a handful of water and began to pour it on the right side of his head and then on the left side. He then took water in both his hands together and poured it on his head