Sunan An-Nasai, Chapter: The Book of Purification

"Uthman called for water for Wudu. He washed his hands three times, then he rinsed his mouth and nose, then he washed his right hand up to the elbow three times. Then he washed his left hand likewise. Then he wiped his head, then he washed his right foot up to the ankle three times, and he washed his left foot likewise. Then he said: 'I saw the Messenger of Allah (saw) performing Wudu as I have just done.' Then he said: "The Messenger of Allah (saw) performs Wudu as I have just done, then prays two Rak'ahs without letting his thoughts wander, his previous sins will be forgiven.'" (Sahih)