Musnad Ahmad 3:38

Safwan ibn ‘Isa narrated to us, from Muhammad ibn ‘Abdullah ibn Abi Maryam, who said: I entered upon Ibn Darah, the freed slave of ‘Uthman. He heard me rinsing my mouth, so he said: "O Muhammad." I said: "At your service." He said: "Shall I not tell you about the ablution of the Messenger of Allah, may Allah bless him and grant him peace?" He said: "I saw ‘Uthman while he was at the Maqa‘id (a place in Medina). He called for water for ablution, so he rinsed his mouth three times, inhaled water into his nose three times, washed his face three times, and his forearms three times each. He wiped his head three times, and washed his feet. Then he said: 'Whoever wishes to look at the ablution of the Messenger of Allah, may Allah bless him and grant him peace, then this is the ablution of the Messenger of Allah, may Allah bless him and grant him peace.'"