That he was riding a horse on the day, the Muslims fought (against the Byzantines), and the commander of the Muslim army was Khalid bin Al-Walid who had been appointed by Abu Bakr. The enemy took the horse away, and when the enemy was defeated, Khalid returned the horse to him.
أَنَّهُ كَانَ عَلَى فَرَسٍ يَوْمَ لَقِيَ الْمُسْلِمُونَ وَأَمِيرُ الْمُسْلِمِينَ يَوْمَئِذٍ خَالِدُ بْنُ الْوَلِيدِ بَعَثَهُ أَبُو بَكْرٍ فَأَخَذَهُ الْعَدُوُّ فَلَمَّا هُزِمَ الْعَدُوُّ رَدَّ خَالِدٌ فَرَسَهُ