Sahih Bukhari Volume 2, Book 15, Hadith Number 71

Narated By Al-Bara’ : 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).”