Language:
كتاب الصلاة
8  
Prayers (Salat)
(58)
Chapter: Sleeping of a men in the mosque
(58)
باب نَوْمِ الرِّجَالِ فِي الْمَسْجِدِ
Sahih al-Bukhari 442

Narrated Abu Huraira:

I saw seventy of As-Suffa men and none of them had a Rida' (a garment covering the upper part of the body). They had either Izars (only) or sheets which they tied round their necks. Some of these sheets reached the middle of their legs and some reached their heels and they used to gather them with their hands lest their private parts should become naked.

حَدَّثَنَا يُوسُفُ بْنُ عِيسَى، قَالَ حَدَّثَنَا ابْنُ فُضَيْلٍ، عَنْ أَبِيهِ، عَنْ أَبِي حَازِمٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ رَأَيْتُ سَبْعِينَ مِنْ أَصْحَابِ الصُّفَّةِ، مَا مِنْهُمْ رَجُلٌ عَلَيْهِ رِدَاءٌ، إِمَّا إِزَارٌ وَإِمَّا كِسَاءٌ، قَدْ رَبَطُوا فِي أَعْنَاقِهِمْ، فَمِنْهَا مَا يَبْلُغُ نِصْفَ السَّاقَيْنِ، وَمِنْهَا مَا يَبْلُغُ الْكَعْبَيْنِ، فَيَجْمَعُهُ بِيَدِهِ، كَرَاهِيَةَ أَنْ تُرَى عَوْرَتُهُ‏.‏
Reference : Sahih al-Bukhari 442
In-book reference : Book 8, Hadith 91
USC-MSA web (English) reference : Vol. 1, Book 8, Hadith 433
  (deprecated numbering scheme)