Sahih al-Bukhari, Volume 5, Book 59, Hadith 461 (USC-MSA) ⓘ
Narrated Jabir bin `Abdullah Al-Ansari: I saw the Prophet offering his Nawafil prayer on his Mount facing the East during the Ghazwa of Anmar.
حَدَّثَنَا آدَمُ، حَدَّثَنَا ابْنُ أَبِي ذِئْبٍ، حَدَّثَنَا عُثْمَانُ بْنُ عَبْدِ اللَّهِ بْنِ سُرَاقَةَ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ الأَنْصَارِيِّ، قَالَ رَأَيْتُ النَّبِيَّ صلى الله عليه وسلم فِي غَزْوَةِ أَنْمَارٍ يُصَلِّي عَلَى رَاحِلَتِهِ، مُتَوَجِّهًا قِبَلَ الْمَشْرِقِ مُتَطَوِّعًا.
also referenced under: Book 64, Hadith 184 (In-Book) & Hadith 4140 (DarusSalam)