Sahih Bukhari Volume 4, Book 56, Hadith 3070

حَدَّثَنَا أَحْمَدُ بْنُ يُونُسَ، حَدَّثَنَا زُهَيْرٌ، عَنْ مُوسَى بْنِ عُقْبَةَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما أَنَّهُ كَانَ عَلَى فَرَسٍ يَوْمَ لَقِيَ الْمُسْلِمُونَ، وَأَمِيرُ الْمُسْلِمِينَ يَوْمَئِذٍ خَالِدُ بْنُ الْوَلِيدِ، بَعَثَهُ أَبُو بَكْرٍ، فَأَخَذَهُ الْعَدُوُّ، فَلَمَّا هُزِمَ الْعَدُوُّ رَدَّ خَالِدٌ فَرَسَهُ‏

Narrated By Ibn Umar : 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.