It was narrated that Shaqiq bin Salamah said:
"I saw `Uthman and `Ali performing ablution, washing each part three times, and they said: 'This is how the Messenger of Allah used to perform ablution.'" (Hasan)Another chain with similar wording. (IT)
English reference (IT): Vol. 1, Book 1, Hadith 413 (IT)
Arabic reference (IT): Book 1, Hadith 447 (IT)