سُنَنُ أَبِي دَاوُدَ
Sunan Abi Dawud 125
Purification (Kitab Al-Taharah)
The Manner of The Prophet's Wudu'
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.
Sunan Abi Dawud, 125Sahih (Al-Albani)صحيح (الألباني)