Musnad Ahmad 3:89

Ibn al-Ashja‘i narrated to us, my father narrated to us, from Sufyan, from Salim Abu al-Nadr, from Busr ibn Sa‘id, who said: ‘Uthman came to the seats (al-maqā‘id), and he called for water for ablution. He rinsed his mouth and sniffed water into his nose, then he washed his face three times, and his hands three times each. Then he wiped his head and [washed] his feet three times each. Then he said: "I saw the Messenger of Allah, peace and blessings of Allah be upon him, perform ablution like this. O you people, is it like that?" They said: "Yes," to a group of the companions of the Messenger of Allah who were with him.