كتاب الطهارة
2  
The Book of Purification
(22)
Chapter: Wiping over the khuff (leather socks)
(22)
باب الْمَسْحِ عَلَى الْخُفَّيْنِ ‏‏
Sahih Muslim 274c

Mughira b. Shu'ba reported:

I was with the Messenger of Allah (ﷺ) one night. He came down (from the ride) and relieved himself. He then came and I poured water upon him from the jar that I carried with me. He performed ablution and wiped over his socks.
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى التَّمِيمِيُّ، أَخْبَرَنَا أَبُو الأَحْوَصِ، عَنْ أَشْعَثَ، عَنِ الأَسْوَدِ بْنِ هِلاَلٍ، عَنِ الْمُغِيرَةِ بْنِ شُعْبَةَ، قَالَ بَيْنَا أَنَا مَعَ، رَسُولِ اللَّهِ صلى الله عليه وسلم ذَاتَ لَيْلَةٍ إِذْ نَزَلَ فَقَضَى حَاجَتَهُ ثُمَّ جَاءَ فَصَبَبْتُ عَلَيْهِ مِنْ إِدَاوَةٍ كَانَتْ مَعِي فَتَوَضَّأَ وَمَسَحَ عَلَى خُفَّيْهِ ‏.‏
Reference : Sahih Muslim 274c
In-book reference : Book 2, Hadith 95
USC-MSA web (English) reference : Book 2, Hadith 526
  (deprecated numbering scheme)