Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 106
Narated By Humran b. Abban, the freed slave of 'Uthman : I saw 'Uthman b. 'Affan while he performed ablution. He poured water over his hands three times and then washed them. He then rinsed his mouth and then cleaned his nose with water (three times). He then washed his right arm upto the elbow three times, then washed his left arm in a similar manner; then wiped his head; then washed his right foot three times, then his left foot in a similar manner, and then said: I saw the Apostle of Allah (pbuh) performing ablution like this ablution of mine. Then he (the Prophet) said: He who performs ablution like this ablution of mine and then offered two Rak'ahs of prayer without allowing his thoughts to be distracted, Allah will pardon all his previous sins.