Sunan an-Nasa'i, Hadith 1686 ⓘ
It was narrated from Ibn Umar that: The Messenger of Allah used to pray witr on his mount.
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 .
also referenced under: Book 20, Hadith 89 (In-Book) & Volume 2, Book 20, Hadith 1687 (DarusSalam)