Sahih al-Bukhari — Fighting for the Cause of Allah (Jihaad) — Hadith No: 3069
Translation
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