Language:
كتاب الصلاة
8  
Prayers (Salat)
(50)
Chapter: To offer As-Salat (the prayer) in the camel yards (the places where the camels are stationed)
(50)
باب الصَّلاَةِ فِي مَوَاضِعِ الإِبِلِ
Sahih al-Bukhari 430

Narrated Nafi`:

"I saw Ibn `Umar praying while taking his camel as a Sutra in front of him and he said, "I saw the Prophet doing the same."

حَدَّثَنَا صَدَقَةُ بْنُ الْفَضْلِ، قَالَ أَخْبَرَنَا سُلَيْمَانُ بْنُ حَيَّانَ، قَالَ حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ نَافِعٍ، قَالَ رَأَيْتُ ابْنَ عُمَرَ يُصَلِّي إِلَى بَعِيرِهِ وَقَالَ رَأَيْتُ النَّبِيَّ صلى الله عليه وسلم يَفْعَلُهُ‏.‏
Reference : Sahih al-Bukhari 430
In-book reference : Book 8, Hadith 80
USC-MSA web (English) reference : Vol. 1, Book 8, Hadith 422
  (deprecated numbering scheme)