Narrated Al-Bara':

I heard the Prophet ﷺ delivering a Khutba saying, "The first thing to be done on this day (first day of 'Id ul Adha) is to pray;
and after returning from the prayer we slaughter our sacrifices (in the name of Allah) and whoever does so, he acted according to our Sunna (traditions)."

حَدَّثَنَا حَجَّاجٌ، قَالَ حَدَّثَنَا شُعْبَةُ، قَالَ أَخْبَرَنِي زُبَيْدٌ، قَالَ سَمِعْتُ الشَّعْبِيَّ، عَنِ الْبَرَاءِ، قَالَ سَمِعْتُ النَّبِيَّ ﷺ يَخْطُبُ فَقَالَ " إِنَّ أَوَّلَ مَا نَبْدَأُ مِنْ يَوْمِنَا هَذَا أَنْ نُصَلِّيَ، ثُمَّ نَرْجِعَ فَنَنْحَرَ، فَمَنْ فَعَلَ فَقَدْ أَصَابَ سُنَّتَنَا ".