Anas · The Book of Sacrifices

He who slaughtered (the animal as a sacrifice) before the ('Id) prayer. should repeat it (i. e. offer another animal). Thereupon a person stood up and said: Messenger of Allah, that is the day when meat is much desired, and he also made a mention of the need of his neighbour, and perhaps Allah's Messenger (ﷺ) attested it. He (the person who had sacrificed the animal before the 'Id prayer) said: I have a goat of less than one year…

He who slaughtered the animal before prayer should slaughter (another animal as a sacrifice). The rest of the hadith is the same.

Allah's Messenger (ﷺ) addressed us on the day of 'Id al-Adha. He smelt the odour of flesh and he prohibited thern from slaughtering (the animals before the 'Id prayer), saying: He who slaughtered the animals (before the 'Id prayer) should do that again (as it is not valid as a sacrifice).

I saw him sacrificing them with his own hand and saw him placing his foot on their sides, and recited the name of Allah and Glorified Him.