That he witnessed the Prophet ﷺ on the Day of Nahr. The Prophet ﷺ offered prayer and then delivered a sermon saying, "Whoever slaughtered his sacrifice before offering prayer, should slaughter another animal in place of the first; and whoever has not yet slaughtered any, should slaughter a sacrifice and mention Allah's Name while doing so."
أَنَّهُ شَهِدَ النَّبِيَّ ﷺ يَوْمَ النَّحْرِ صَلَّى ثُمَّ خَطَبَ فَقَالَ مَنْ ذَبَحَ قَبْلَ أَنْ يُصَلِّيَ فَلْيَذْبَحْ مَكَانَهَا أُخْرَى وَمَنْ لَمْ يَذْبَحْ فَلْيَذْبَحْ بِاسْمِ اللَّهِ