(4) باب جَوَازِ صَلاَةِ النَّافِلَةِ عَلَى الدَّابَّةِ فِي السَّفَرِ حَيْثُ تَوَجَّهَتْ
Ibn 'Umar reported:
I saw the Messenger of Allah (ﷺ) praying (Nafl prayer) on a donkey's back while his face was turned towards Khaibar.
Reference: Sahih Muslim 700 e
In-book reference: Book 6, Hadith 45
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1501