أَخْبَرَنَا عُبَيْدُ اللَّهِ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ الأَخْنَسِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يُوتِرُ عَلَى الرَّاحِلَةِ ‏.‏

It was narrated from Ibn Umar that: The Messenger of Allah (PBUH) used to pray witr on his mount. Translation Not Available

Book Ref: Sunan An Nisai Book 20 Hadith 1686
Web Ref:  Sunan An Nisai Vol 2 Book 20 Hadith 1687