Sahih al-Bukhari 1072
In-book no 1072وَقَالَ اللَّيْثُ حَدَّثَنِي يُونُسُ، عَنِ ابْنِ شِهَابٍ، قَالَ حَدَّثَنِي عَبْدُ اللَّهِ بْنُ عَامِرٍ، أَنَّ أَبَاهُ، أَخْبَرَهُ أَنَّهُ، رَأَى النَّبِيَّ صلى الله عليه وسلم صَلَّى السُّبْحَةَ بِاللَّيْلِ فِي السَّفَرِ عَلَى ظَهْرِ رَاحِلَتِهِ حَيْثُ تَوَجَّهَتْ بِهِ.
Narrated `Abdullah bin Amir that his father had told him that he had seen the Prophet (p.b.u.h) praying Nawafil at night on the back of his Mount on a journey, facing whatever direction it took.