Mishkat al-Masabih 20 Game and Animals Which May Be Slaughtered كتاب الصيد والذبائح 17

وَعَنْ هِشَامِ بْنِ زَيْدٍ عَنْ أَنَسٍ قَالَ: دَخَلْتُ عَلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَهُوَ فِي مِرْبَدٍ فَرَأَيْتُهُ يَسِمُ شَاءَ حسبته قَالَ: فِي آذانها

Hisham b. Zaid quoted Anas as saying that he went to visit the Prophet when he was in an enclosure and saw him branding sheep. He thought he said it was on their ears. (Bukhari and Muslim.)