Language:
كتاب الصلاة
8  
Prayers (Salat)
(10)
Chapter: What may be used to cover the private parts of the body
(10)
باب مَا يَسْتُرُ مِنَ الْعَوْرَةِ
Sahih al-Bukhari 367

Narrated Abu Sa`id Al-Khudri:

Allah's Messenger (ﷺ) forbade Ishtimal-As-Samma' (wrapping one's body with a garment so that one cannot raise its end or take one's hand out of it). He also forbade Al-Ihtiba' (sitting on buttocks with knees close to `Abdomen and feet apart with the hands circling the knees) while wrapping oneself with a single garment, without having a part of it over the private parts.

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا لَيْثٌ، عَنِ ابْنِ شِهَابٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ بْنِ عُتْبَةَ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، أَنَّهُ قَالَ نَهَى رَسُولُ اللَّهِ صلى الله عليه وسلم عَنِ اشْتِمَالِ الصَّمَّاءِ وَأَنْ يَحْتَبِيَ الرَّجُلُ فِي ثَوْبٍ وَاحِدٍ، لَيْسَ عَلَى فَرْجِهِ مِنْهُ شَىْءٌ‏.‏
Reference : Sahih al-Bukhari 367
In-book reference : Book 8, Hadith 19
USC-MSA web (English) reference : Vol. 1, Book 8, Hadith 363
  (deprecated numbering scheme)