It was narrated that ‘Ali (رضي الله عنه) said:
The Messenger of Allah (ﷺ) instructed us to check the eyes and ears, and not to sacrifice any animal whose ears are slit in two lengthwise, any animal that has a round hole in its ear as a distinguishing mark, any animal that has the edge of its ears cut, or any animal whose ears were slit from the back.