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 : Book 56, Hadith 275 USC-MSA web (English) : Vol. 4, Book 52, Hadith 303 (deprecated)
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