I witnessed the Prophet ﷺ offering the ʿId 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."
شَهِدْتُ النَّبِيَّ ﷺ صَلَّى يَوْمَ عِيدٍ ثُمَّ خَطَبَ ثُمَّ قَالَ مَنْ ذَبَحَ فَلْيُبَدِّلْ مَكَانَهَا وَمَنْ لَمْ يَكُنْ ذَبَحَ فَلْيَذْبَحْ بِاسْمِ اللَّهِ
On the day of Nahr the Prophet ﷺ offered the prayer and delivered the Khutba and then slaughtered the sacrifice and said, "Anybody who slaughtered (his sacrifice) before the prayer should slaughter another animal in lieu of it, and the one who has not yet slaughtered should slaughter the sacrifice mentioning Allah's name on it."
صَلَّى النَّبِيُّ ﷺ يَوْمَ النَّحْرِ ثُمَّ خَطَبَ ثُمَّ ذَبَحَ فَقَالَ مَنْ ذَبَحَ قَبْلَ أَنْ يُصَلِّيَ فَلْيَذْبَحْ أُخْرَى مَكَانَهَا وَمَنْ لَمْ يَذْبَحْ فَلْيَذْبَحْ بِاسْمِ اللَّهِ
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.
شَهِدْتُ رَسُولَ اللَّهِ ﷺ صَلَّى يَوْمَ أَضْحًى ثُمَّ خَطَبَ فَقَالَ مَنْ كَانَ ذَبَحَ قَبْلَ أَنْ يُصَلِّيَ فَلْيُعِدْ مَكَانَهَا وَمَنْ لَمْ يَكُنْ ذَبَحَ فَلْيَذْبَحْ بِاسْمِ اللَّهِ
[Machine] I heard Jundub saying, "I witnessed the Prophet ﷺ and then he delivered a sermon and said, 'Whoever has slaughtered a sacrifice before offering prayers, then let him slaughter again and replace it in its place. And whoever has not slaughtered, then let him slaughter in the name of Allah.'"
سَمِعْتُ جُنْدُبًا يَقُولُ شَهِدْتُ النَّبِيَّ ﷺ ثُمَّ خَطَبَ فَقَالَ «مَنْ كَانَ ذَبَحَ قَبْلَ أَنْ يُصَلِّيَ فَلْيَذْبَحْ وَلْيُبْدِلْ مَكَانَهَا وَمَنْ لَمْ يَكُنْ ذَبَحَ فَلْيَذْبَحْ بِاسْمِ اللهِ»