(187) باب إِذَا غَنِمَ الْمُشْرِكُونَ مَالَ الْمُسْلِمِ ثُمَّ وَجَدَهُ الْمُسْلِمُ
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.
Reference: Sahih al-Bukhari 3069
In-book reference: Book 56, Hadith 275
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 4, Book 52, Hadith 303