The Prophet (p.b.u.h) said, "The first thing that we should do on this day of ours is to pray and then
return to slaughter the sacrifice. So anyone who does so, he acted according to our Sunna (tradition),
and whoever slaughtered the sacrifice before the prayer, it was just meat which he presented to his
family and would not be considered as Nusuk." A person from the Ansar named Abu Burda bin
Niyyar said, "O Allah's Messenger (ﷺ)! I slaughtered the Nusuk (before the prayer) but I have a young shegoat
which is better than an older sheep." The Prophet (ﷺ) I said, "Sacrifice it in lieu of the first, but it will
be not sufficient (as a sacrifice) for anybody else after you."
Sahih al-Bukhari Book 13, Hadith 14