Musannaf Ibn Abi Shayba 1:65

Abu Mu'awiyah narrated to us, from Hajjaj, from 'Ata', that 'Uthman performed ablution three times [for each part], and wiped his head with one wiping, and washed his feet with washing. Then he said: "This is how I saw the Messenger of Allah (may Allah bless him and grant him peace) perform ablution."