"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.'"
Jami` at-Tirmidhi Book 19, Hadith 15
← Previous Hadith "Ali said: 'A cow is for seven.' I said: "And if it gives birth?' He said: 'Then slaughter its offspring with it.' I said: 'What if it is lame?' He said: 'When it has reached the place of ritual.' I said: 'What if it has a broken horn?' He said: 'There is no harm, we were ordered' - or - 'The Messenger of Allah (ﷺ) ordered us, to check the two eyes and the two ears.'"

Jami` at-Tirmidhi Book 19, Hadith 14 Next Hadith → "I asked Abu Abyub how the slaughtering was done during the time of the Messenger of Allah (ﷺ). He said: 'A man would sacrifice a sheep for himself and the people in his household. They would eat from it and feed others, until the people (later) would boast about it and it became as you see now."

Jami` at-Tirmidhi Book 19, Hadith 16