I was with Messenger of Allah ﷺ (on the occasion) of 'Id al-Adha. After he had completed the prayer with people, he found that the goats had been slaughtered, whereupon he said: He who slaughtered sacrificial animal before the prayer should slaughter a goat (again) in its stead and he who has not slaughtered he should slaughter it by reciting the name of Allah.

شَهِدْتُ الأَضْحَى مَعَ رَسُولِ اللَّهِ ﷺ فَلَمَّا قَضَى صَلاَتَهُ بِالنَّاسِ نَظَرَ إِلَى غَنَمٍ قَدْ ذُبِحَتْ فَقَالَ مَنْ ذَبَحَ قَبْلَ الصَّلاَةِ فَلْيَذْبَحْ شَاةً مَكَانَهَا وَمَنْ لَمْ يَكُنْ ذَبَحَ فَلْيَذْبَحْ عَلَى اسْمِ اللَّهِ