Sahih Muslim 273a
Sahih Muslim · Book 2: The Book of Purification · Wiping over the khuff (leather socks)
Hudhaifa reported:
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى التَّمِيمِيُّ ، أَخْبَرَنَا أَبُو خَيْثَمَةَ ، عَنِ الأَعْمَشِ ، عَنْ شَقِيقٍ ، عَنْ حُذَيْفَةَ ، قَالَ كُنْتُ مَعَ النَّبِيِّ صلى الله عليه وسلم فَانْتَهَى إِلَى سُبَاطَةِ قَوْمٍ فَبَالَ قَائِمًا فَتَنَحَّيْتُ فَقَالَ " ادْنُهْ " . فَدَنَوْتُ حَتَّى قُمْتُ عِنْدَ عَقِبَيْهِ فَتَوَضَّأَ فَمَسَحَ عَلَى خُفَّيْهِ .
I was with the Messenger of Allah (ﷺ) when he came to the dumping ground of filth belonging to a particular tribe. He urinated while standing, and I went aside. He (the Holy Prophet) asked me to come near him and I went so near to him that I stood behind his heels. He then performed ablution and wiped over his socks.