Musnad Ahmad 5:632

Abdullah narrated to us, Zakariya ibn Yahya Zahmuwayh narrated to us, Sharik narrated to us, from Khalid ibn Alqamah, from Abd Khayr, who said: We prayed the morning prayer, then we sat with Ali ibn Abi Talib. He called for water for ablution, so he washed his hands three times, and rinsed his mouth twice from a single handful. Then he washed his face three times, then he washed his forearms, then he washed his feet three times. Then he said: "This is the ablution of your Prophet, may Allah bless him and grant him peace, so know it."