Sunan Ibn Majah 1201
سنن ابن ماجه#1201Sahihحَدَّثَنَا مُحَمَّدُ بْنُ يَزِيدَ الأَسْفَاطِيُّ، حَدَّثَنَا أَبُو دَاوُدَ، حَدَّثَنَا عَبَّادُ بْنُ مَنْصُورٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ النَّبِيَّ ـ صلى الله عليه وسلم ـ كَانَ يُوتِرُ عَلَى رَاحِلَتِهِ .
It was narrated from Ibn ‘Abbas that the Prophet (ﷺ) used to pray Witr while riding his mount
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih Lighairihi
Zubair Ali ZaiSahih
In-book reference: 5:399