Muhammad bin Abdullah bin Abi Maryam said: I went to Ibn Darah, the freed slave of Sayyiduna Uthman (may Allah be pleased with him), at his house, and he heard me rinsing my mouth. Then he said: O Muhammad! I said: Yes! He said: Shall I not tell you about the ablution of the Messenger of Allah (peace and blessings be upon him)? I said: Of course! He said: I saw Sayyiduna Uthman bin Affan (may Allah be pleased with him) at the place of sitting (al-Maqa'id). He called for a vessel, then rinsed his mouth three times, sniffed water into his nose three times, washed his face and his forearms three times, wiped his head three times, then washed his feet. Then he said: Whoever would like to see the manner of ablution of the Messenger of Allah (peace and blessings be upon him), let him look at this ablution of mine. Others (other narrators) besides him have also mentioned washing the feet three times.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 294