Sahih al-Bukhari, Volume 1, Book 8, Hadith 422 (USC-MSA) ⓘ
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.
also referenced under: Book 8, Hadith 80 (In-Book) & Hadith 430 (DarusSalam)