The Messenger of Allah (ﷺ) used to sacrifice a choice, horned ram with black round the eyes, the mouth and the feet.
Sunan Abi Dawud Book 16, Hadith 9
← Previous Hadith The Prophet (ﷺ) sacrificed two horned rams which were white with black markings and had been castrated. When he made them face the qiblah, he said: I have turned my face towards Him. Who created the heavens and the earth, following Abraham's religion, the true in faith, and I am not one of the polytheists. My prayer, and my service of sacrifice, my life and my death are all for Allah, the Lord of the Universe, Who has no partner. That is what I was commanded to do, and I am one of the Muslims. O Allah it comes from Thee and is given to Thee from Muhammad and his people. In the name of Allah, and Allah is Most Great. He then made sacrifice.

Sunan Abi Dawud Book 16, Hadith 8 Next Hadith → The Messenger of Allah (ﷺ) as saying: Sacrifice only a full-grown animal unless it is difficult for you, in which case sacrifice a lamb.

Sunan Abi Dawud Book 16, Hadith 10