Musnad Ahmad 5:443

Waki' narrated to us, al-Hasan ibn 'Uqbah Abu Kabran al-Muradi narrated to us, I heard 'Abd Khayr saying: 'Ali said: "Shall I not show you the ablution of the Messenger of Allah, may Allah bless him and grant him peace?" Then he performed ablution three times [for each part].