Volume 7 · Book 67 · Hadith 450
Narrated Anas: I brought a brother of mine to the Prophet to do Tahnik for him while the Prophet was in a sheep fold of his, and I saw him branding a sheep. (The sub-narrator said: I think Anas said, branding it on the ear.)
— Sahih Bukhari, Volume 7, Book 67: Hunting, Slaughtering, Hadith #450