Sahih al-Bukhari 951Book 13, Hadith 3
حَدَّثَنَا حَجَّاجٌ، قَالَ حَدَّثَنَا شُعْبَةُ، قَالَ أَخْبَرَنِي زُبَيْدٌ، قَالَ سَمِعْتُ الشَّعْبِيَّ، عَنِ الْبَرَاءِ، قَالَ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَخْطُبُ فَقَالَ " إِنَّ أَوَّلَ مَا نَبْدَأُ مِنْ يَوْمِنَا هَذَا أَنْ نُصَلِّيَ، ثُمَّ نَرْجِعَ فَنَنْحَرَ، فَمَنْ فَعَلَ فَقَدْ أَصَابَ سُنَّتَنَا ".
I heard the Prophet (p.b.u.h) 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)."