I witnessed the Prophet (ﷺ) offering the `Id prayer (and after finishing it) he delivered a sermon and said, "Whoever has slaughtered his sacrifice (before the prayer) should make up for it (i.e. slaughter another animal) and whoever has not slaughtered his sacrifice yet, should slaughter it by mentioning Allah's Name over it."
Sahih al-Bukhari Book 83, Hadith 52
← Previous Hadith Narrated Al-Bara bin Azib that once he had a guest, so he told his family (on the Day of Id-ul-Adha) that they should slaughter the animal for sacrifice before he returned from the ('Id) prayer in order that their guest could take his meal. So his family slaughtered (the animal ) before the prayer. Then they mentioned that event to the Prophet who ordered Al-Bara to slaughter another sacrifice. Al-Bara' said to the Prophet (ﷺ) , "I have a young milch she-goat which is better than two sheep for slaughtering." (The sub-narrator, Ibn 'Aun used to say, "I don't know whether the permission (to slaughter a she-goat as a sacrifice) was especially given to Al-Bara' or if it was in general for all the Muslims.") (See Hadith No. 99, Vol. 2.)

Sahih al-Bukhari Book 83, Hadith 51 Next Hadith → The Prophet (ﷺ) said, "The biggest sins are: To join others in worship with Allah; to be undutiful to one's parents; to kill somebody unlawfully; and to take an oath Al-Ghamus.

Sahih al-Bukhari Book 83, Hadith 53