Sahih al-Bukhari 400

Arabic

حَدَّثَنَا مُسْلِمٌ، قَالَ حَدَّثَنَا هِشَامٌ، قَالَ حَدَّثَنَا يَحْيَى بْنُ أَبِي كَثِيرٍ، عَنْ مُحَمَّدِ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ جَابِرٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي عَلَى رَاحِلَتِهِ حَيْثُ تَوَجَّهَتْ، فَإِذَا أَرَادَ الْفَرِيضَةَ نَزَلَ فَاسْتَقْبَلَ الْقِبْلَةَ‏.‏

English translation

Narrated Jabir:Allah's Messenger (ﷺ) used to pray (optional, non-obligatory prayer) while riding on his mount (Rahila) wherever it turned, and whenever he wanted to pray the compulsory prayer he dismounted and prayed facing the Qibla

Reference: Sahih al-Bukhari 400, Book of Prayers (Salat). English translation by Dr. Muhammad Muhsin Khan.