´Narrated 'Ali:` "The Messenger of Allah (ﷺ) prohibited that an animal with a A'dab (stump) horn or ear should be slaughtered as a sacrifice." Qatadah (one of the narrators) said: "So I mentioned this to Sa'eed bin Al-Musayyab and he said: 'The A'dab is that which equals or more than that.'"
Hadith Referenceسنن ترمذي / كتاب الأضاحى عن رسول الله صلى الله عليه وسلم / 1504