Bukhari Collection: ::Book Number 4:: Hadith # 302
Narrated Nafi`:Once a slave of Ibn `Umar fled and joined the Byzantine. Khalid bin Al-Walid got him back and returned him to `Abdullah (bin `Umar). Once a horse of Ibn `Umar also ran away and followed the Byzantines, and he (i.e. Khalid) got it back and returned it to `Abdullah.