Musnad Ahmad 3:128

'Abdullah narrated to us, Muhammad ibn Abi Bakr al-Muqaddami and Abu al-Rabi' al-Zahrani narrated to me, they said: Hammad ibn Zayd narrated to us, from al-Hajjaj, from 'Ata', from 'Uthman, who said: I saw the Messenger of Allah (peace and blessings of Allah be upon him) perform ablution. He washed his face three times, and his hands three times, and he washed his forearms three times each. He wiped his head, and he washed his feet, washing them.