عَنْ أَنَسٍ: أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ صَلَّى الظُّهْرَ بِالْمَدِينَةِ أَرْبَعًا وَصَلَّى الْعَصْر بِذِي الحليفة رَكْعَتَيْنِ

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.)