Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 115
Narated By 'Abd al-Rahman b. Abi Laila : I saw 'Ali performing ablution. He washed his face three times and his hands three times and wiped his head once. Then he ('Ali) said: The Apostle of Allah (pbuh) used to perform ablution in this way.