Purification (Kitab Al-Taharah)
1/51. Chapter:
The Manner of The Prophet's Wudu'
Sunan Abi Dawud
حَدَّثَنَا مَحْمُودُ بْنُ خَالِدٍ، حَدَّثَنَا الْوَلِيدُ، بِهَذَا الإِسْنَادِ قَالَ فَتَوَضَّأَ ثَلاَثًا ثَلاَثًا وَغَسَلَ رِجْلَيْهِ بِغَيْرِ عَدَدٍ .
Another version says: He performed each part of the ablution three times and washed his feet times without number.
Reference : Sunan Abi Dawud 125In-book reference : Book 1, Hadith 125English translation : Book 1, Hadith 125