The washing of the body parts (i.e., the parts which are washed in ablution) once only while performing ablution

Sahih al-Bukhari · Book 4 · Hadith 157

حَدَّثَنَا مُحَمَّدُ بْنُ يُوسُفَ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ عَطَاءِ بْنِ يَسَارٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ تَوَضَّأَ النَّبِيُّ صلى الله عليه وسلم مَرَّةً مَرَّةً‏.‏

Narrated Ibn `Abbas: The Prophet (ﷺ) performed ablution by washing the body parts only once.