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. (DE)
English reference (DE): Vol. 1, Book 1, Hadith 413 (DE)
Arabic reference (DE): Book 1, Hadith 447 (DE)