كتاب الصلاة
4  
The Book of Prayers
(47)
Chapter: The Sutrah (Screen) For One Who Is Praying, And The Recommendation To Pray Facing A Sutrah. The Ruling On Passing In Front Of One Who Is Praying, And Preventing One Who Wants To Pass In Front. It Is Permissible To Lie Down In Front Of One Who Is Praying, Praying Towards One's Mount. The Command To Stand Close To The Sutrah. The Height Of The Suirah, And Related Matters
(47)
باب سُتْرَةِ الْمُصَلِّي ‏
Sahih Muslim 502 b

Ibn 'Umar reported:

The Apostle of Allah (ﷺ) used to say prayer towards his camel. Ibn Numair said: The Apostle of Allah (ﷺ) said prayer towards the camel.
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَابْنُ، نُمَيْرٍ قَالاَ حَدَّثَنَا أَبُو خَالِدٍ الأَحْمَرُ، عَنْ عُبَيْدِ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يُصَلِّي إِلَى رَاحِلَتِهِ ‏.‏ وَقَالَ ابْنُ نُمَيْرٍ إِنَّ النَّبِيَّ صلى الله عليه وسلم صَلَّى إِلَى بَعِيرٍ ‏.‏
Reference : Sahih Muslim 502b
In-book reference : Book 4, Hadith 280
USC-MSA web (English) reference : Book 4, Hadith 1013
  (deprecated numbering scheme)