Musannaf Ibn Abi Shayba 1:1060

Abu Bakr narrated to us, he said: Abu Bakr ibn Ayyash narrated to us, he said: Abu Ishaq narrated to us, from al-Harith, from Ali, who said: He called for water, then he washed his hands three times before he inserted them into the vessel. Then he said: "This is how I saw the Messenger of Allah, may Allah bless him and grant him peace, do."