Musnad Ahmad 3:6

Waki’ narrated to us, Sufyan narrated to us, from Abu al-Nadr, from Abu Anas: That Uthman performed ablution at al-Maqa’id, three times each. There were men from the companions of the Messenger of Allah, peace and blessings of Allah be upon him, with him. He said: "Is this not how you saw the Messenger of Allah, peace and blessings of Allah be upon him, perform ablution?" They said: "Yes."