The Book Pertaining to Clothes and Decoration (Kitab Al-Libas wa'l-Zinah)
Muslim :: Book 24 : Hadith 5287
Anas reported: We went to Allah's Messenger (may peace be upon him) as he was in the fold and he was cauterising the animals of the flock and I think (he was cauterising them) on their ears. This hadith has been narrated on the authority of Shu'ba through another chain of transmitters.