Sahih al-Bukhari 1096
Sahih al-Bukhari · Book 18: Shortening the Prayers (At-Taqseer) · To offer the Salat by signs (while riding) on an animal
Narrated `Abdullah bin Dinar:
حَدَّثَنَا مُوسَى ، قَالَ حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ مُسْلِمٍ ، قَالَ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ دِينَارٍ ، قَالَ كَانَ عَبْدُ اللَّهِ بْنُ عُمَرَ ـ رضى الله عنهما ـ يُصَلِّي فِي السَّفَرِ عَلَى رَاحِلَتِهِ، أَيْنَمَا تَوَجَّهَتْ يُومِئُ. وَذَكَرَ عَبْدُ اللَّهِ أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يَفْعَلُهُ.
On traveling, `Abdullah bin `Umar used to offer the prayer on his Mount by signs whatever direction it took. `Abdullah said that the Prophet (ﷺ) used to do so.