Ibn Ishaq محمد بن إسحاق بن يسار‎ · Sacrifice (Kitab Al-Dahaya)

The Prophet (ﷺ) sacrificed two horned rams which were white with black markings, slaughtered, and uttered: "Allah is Most Great." and mentioned Allah's name and placed his foot on their sides.

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.