I saw Messenger of Allah ﷺ observing ('Id) prayer on the Day of Sacrifice (10th of Dhu'l-Hijja) and then delivering a sermon and he said: He who sacrificed the (animal) before offering ('Id) prayer, he should offer again in its stead, and he who did not sacrifice the animal should slaughter it by reciting the name of Allah. (Using translation from Muslim 1960d)
أَنَّهُ شَهِدَ رَسُولَ اللهِ ﷺ صَلَّى ثُمَّ خَطَبَ فَقَالَ مَنْ كَانَ ذَبَحَ قَبْلَ أَنْ يُصَلِّيَ فَلْيُعِدْ مَكَانَهَا أُخْرَى وَقَالَ مَرَّةً أُخْرَى فَلْيَذْبَحْ وَمَنْ كَانَ لَمْ يَذْبَحْ فَلْيَذْبَحْ بِاسْمِاللهِ