Sahih al Bukhari 206
Ablutions (Wudu')
حَدَّثَنَا أَبُو نُعَيْمٍ، قَالَ حَدَّثَنَا زَكَرِيَّاءُ، عَنْ عَامِرٍ، عَنْ عُرْوَةَ بْنِ الْمُغِيرَةِ، عَنْ أَبِيهِ، قَالَ كُنْتُ مَعَ النَّبِيِّ صلى الله عليه وسلم فِي سَفَرٍ، فَأَهْوَيْتُ لأَنْزِعَ خُفَّيْهِ فَقَالَ " دَعْهُمَا، فَإِنِّي أَدْخَلْتُهُمَا طَاهِرَتَيْنِ ". فَمَسَحَ عَلَيْهِمَا.
Narrated `Urwa bin Al-Mughira:My father said, "Once I was in the company of the Prophet (ﷺ) on a journey and I dashed to take off his Khuffs (socks made from thick fabric or leather). He ordered me to leave them as he had put them after performing ablution. So he passed wet hands over them
Text from the public-domain hadith-api dataset. Numbering follows that dataset and can differ by a few from some printed editions — check the wording, not only the number.