Sahih Bukhari Volume 7, Book 72, Hadith 5544

حَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا شُعْبَةُ، عَنْ هِشَامِ بْنِ زَيْدٍ، عَنْ أَنَسٍ، قَالَ دَخَلْتُ عَلَى النَّبِيِّ صلى الله عليه وسلم بِأَخٍ لِي يُحَنِّكُهُ، وَهْوَ فِي مِرْبَدٍ لَهُ، فَرَأَيْتُهُ يَسِمُ شَاةً ـ حَسِبْتُهُ قَالَ ـ فِي آذَانِهَا‏.‏

Narrated By 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.)