Musnad Ahmad 5:784

Abdullah narrated to us, Sa'id ibn Yahya ibn Sa'id al-Qurashi narrated to me, my father narrated to us, Sufyan narrated to us, from Abu Ishaq, from Abu Hayyah al-Hamdani, who said: Ali ibn Abi Talib, may Allah be pleased with him, said: "Whoever is pleased to look at the ablution of the Messenger of Allah, may Allah bless him and grant him peace, let him look at me." He said: "Then he performed ablution three times [for each part], then he wiped his head, then he drank the remainder of his ablution water."