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

Mughira b. Shu'ba reported:

The Messenger of Allah (ﷺ) went out for relieving himself. When he came back I brought for him a jar (of water) and poured water upon his hands and He washed his face. He tried to wash his forearms, but as the (sleeves of the) gown were tight. He, therefore, brought them out from under the gown. He then washed them, wiped his head, and wiped his socks and then prayed.
وَحَدَّثَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، وَعَلِيُّ بْنُ خَشْرَمٍ، جَمِيعًا عَنْ عِيسَى بْنِ يُونُسَ، - قَالَ إِسْحَاقُ أَخْبَرَنَا عِيسَى، - حَدَّثَنَا الأَعْمَشُ، عَنْ مُسْلِمٍ، عَنْ مَسْرُوقٍ، عَنِ الْمُغِيرَةِ بْنِ شُعْبَةَ، قَالَ خَرَجَ رَسُولُ اللَّهِ صلى الله عليه وسلم لِيَقْضِيَ حَاجَتَهُ فَلَمَّا رَجَعَ تَلَقَّيْتُهُ بِالإِدَاوَةِ فَصَبَبْتُ عَلَيْهِ فَغَسَلَ يَدَيْهِ ثُمَّ غَسَلَ وَجْهَهُ ثُمَّ ذَهَبَ لِيَغْسِلَ ذِرَاعَيْهِ فَضَاقَتِ الْجُبَّةُ فَأَخْرَجَهُمَا مِنْ تَحْتِ الْجُبَّةِ فَغَسَلَهُمَا وَمَسَحَ رَأْسَهُ وَمَسَحَ عَلَى خُفَّيْهِ ثُمَّ صَلَّى بِنَا ‏.‏
Reference : Sahih Muslim 274e
In-book reference : Book 2, Hadith 97
USC-MSA web (English) reference : Book 2, Hadith 528
  (deprecated numbering scheme)