مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 1340
Prayer
Prayer while Travelling - Section 1
وَعَنِ ابْنِ عُمَرَ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُصَلِّي فِي السَّفَرِ عَلَى رَاحِلَتِهِ حَيْثُ تَوَجَّهَتْ بِهِ يُومِئُ إِيمَاءً صَلَاةَ اللَّيْلِ إِلَّا الْفَرَائِضَ وَيُوتِرُ على رَاحِلَته
Ibn ‘Umar said that on a journey God’s Messenger would pray on his riding beast in whatever direction it turned, making a sign with his head* in prayer during the night, but not in the obligatory prayers; and he would observe a witr on his riding beast. *To indicate the bowing and the prostration. (Bukhari and Muslim.)
Mishkat al-Masabih, 1340مُتَّفَقٌ عَلَيْهِ (الألباني)