Sahih al-Bukhari 400
Sahih al-Bukhari · Book 8: Prayers (Salat) · [During the obligatory Salat (prayers)] one should face the Qiblah (Kabah at Makkah) wherever one may be
Narrated Jabir:
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.
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.