Chapter 36: The Book of Sacrifices
Al-Bara' b. 'Azib reported that Abu Burda slaughtered the animal as a sacrifice before the (' Id) prayer. Thereupon Allah' s Apostle (ﷺ) said: Offer a substitute for it (since it does not absolve you of the responsibility of sacrifice). Thereupon he said: Allah' s Messenger. I have nothing with me but a goat of less than six months. Shu' ba (one of the narrators) said: I think he (al-Bara' b. 'Azib also) said: And it is better than a goat of one year. Thereupon Allah' s Messenger (ﷺ) said: Make it a substitute for that (and sacrifice it), but it will not suffice for anyone (as a sacrifice) after you.
Sahih Muslim 1961i