Sahih al-Bukhari 1104
Sahih al-Bukhari · Book 18: Shortening the Prayers (At-Taqseer) · Whoever offered Nawafil not after the compulsory Salat but before it
وَقَالَ 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.