Sahih al-Bukhari, Volume 2, Book 16, Hadith 113 (USC-MSA) ⓘ

Narrated Sa`id bin Yasar: I was going to Mecca in the company of `Abdullah bin `Umar and when I apprehended the approaching dawn, I dismounted and offered the witr prayer and then joined him. `Abdullah bin `Umar said, "Where have you been?" I replied, "I apprehended the approaching dawn so I dismounted and prayed the witr prayer." `Abdullah said, "Isn't it sufficient for you to follow the good example of Allah's Messenger?" I replied, "Yes, by Allah." He said, "Allah's Messenger used to pray witr on the back of the camel (while on a journey)."

حَدَّثَنَا إِسْمَاعِيلُ، قَالَ حَدَّثَنِي مَالِكٌ، عَنْ أَبِي بَكْرِ بْنِ عُمَرَ بْنِ عَبْدِ الرَّحْمَنِ بْنِ عَبْدِ اللَّهِ بْنِ عُمَرَ بْنِ الْخَطَّابِ، عَنْ سَعِيدِ بْنِ يَسَارٍ، أَنَّهُ قَالَ كُنْتُ أَسِيرُ مَعَ عَبْدِ اللَّهِ بْنِ عُمَرَ بِطَرِيقِ مَكَّةَ فَقَالَ سَعِيدٌ فَلَمَّا خَشِيتُ الصُّبْحَ نَزَلْتُ فَأَوْتَرْتُ، ثُمَّ لَحِقْتُهُ فَقَالَ عَبْدُ اللَّهِ بْنُ عُمَرَ أَيْنَ كُنْتَ فَقُلْتُ خَشِيتُ الصُّبْحَ، فَنَزَلْتُ فَأَوْتَرْتُ‏.‏ فَقَالَ عَبْدُ اللَّهِ أَلَيْسَ لَكَ فِي رَسُولِ اللَّهِ صلى الله عليه وسلم أُسْوَةٌ حَسَنَةٌ فَقُلْتُ بَلَى وَاللَّهِ‏.‏ قَالَ فَإِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يُوتِرُ عَلَى الْبَعِيرِ‏.‏