The Division of Spoils and Dishonesty regarding them - Section 1 Mishkat al-Masabih 3992
Arabic hadith text
وَعَنْهُ قَالَ: ذَهَبَتْ فَرَسٌ لَهُ فَأَخَذَهَا الْعَدُوُّ فَظَهَرَ عَلَيْهِمُ الْمُسْلِمُونَ فَرُدَّ عَلَيْهِ فِي زَمَنِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ. وَفِي رِوَايَةٍ: أَبَقَ عَبْدٌ لَهُ فَلَحِقَ بِالرُّومِ فَظَهَرَ عَلَيْهِمُ الْمُسْلِمُونَ فَرَدَّ عَلَيْهِ خَالِدُ بْنُ الْوَلِيدِ بَعْدَ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ. رَوَاهُ الْبُخَارِيُّ
Translation
He told that in the time of God's Messenger a horse of his went off and was taken by the enemy, but when the Muslims conquered them it was returned to him. A version says that after the death of the Prophet a slave of his ran away and joined himself to the Byzantines, and when the Muslims conquered them Khalid b. al-Walid returned him to him. Bukhari transmitted it.