Sahih Muslim Book 24, Hadith Number 5286.

Chapter : It is forbidden to beat the animal on the face or cauterise at the face.

Anas reported that when his mother gave birth to a child they brought that child to Allah’s Messenger (may peace be upon him) so that he might chew some dates and touch his palate with them and Allah’s Apostle (may peace be upon him) was at that time in the fold busy in cauterising the animals Shu’ba said: So far as I know (he was cauterising) their ears.