From Sahih Bukhari (Hadith 955):
Narrated Al-Bara' bin `Azib:The Prophet (ﷺ) delivered the Khutba after offering the prayer on the Day of Nahr and said, "Whoever offers the prayer like us and slaughters like us then his Nusuk (sacrifice) will be accepted by Allah. And whoever slaughters his sacrifice before the `Id prayer then he has not done the sacrifice." Abi Burda bin Niyar, the uncle of Al-Bara' said, "O Allah's Messenger (ﷺ)! I have slaughtered my sheep before the `Id prayer and I thought today as a day of eating and drinking (not alcoholic drinks), and I liked that my sheep should be the first to be slaughtered in my house. So I slaughtered my sheep and took my food before coming for the prayer." The Prophet (ﷺ) said, "The sheep which you have slaughtered is just mutton (not a Nusuk)." He (Abu Burda) said, "O Allah's Messenger (ﷺ)! I have a young she-goat which is dearer to me than two sheep. Will that be sufficient as a Nusuk on my behalf? "The Prophet (ﷺ) said, "Yes, it will be sufficient for you but it will not be sufficient (as a Nusuk) for anyone else after you
Reference: Bukhari 955