Language:
كتاب الجهاد والسير
56  
Fighting for the Cause of Allah (Jihaad)
(187)
Chapter: If Al-Mushrikun take the property of a Muslim as war booty
(187)
باب إِذَا غَنِمَ الْمُشْرِكُونَ مَالَ الْمُسْلِمِ ثُمَّ وَجَدَهُ الْمُسْلِمُ
Sahih al-Bukhari 3069

Narrated 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.

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.‏
Reference : Sahih al-Bukhari 3069
In-book reference : Book 56, Hadith 274
USC-MSA web (English) reference : Vol. 4, Book 52, Hadith 303
  (deprecated numbering scheme)