Sahih Bukhari Volume 2, Book 13, Hadith 966

حَدَّثَنَا آدَمُ، قَالَ حَدَّثَنَا شُعْبَةُ، قَالَ حَدَّثَنَا زُبَيْدٌ، قَالَ سَمِعْتُ الشَّعْبِيَّ، عَنِ الْبَرَاءِ بْنِ عَازِبٍ، قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ إِنَّ أَوَّلَ مَا نَبْدَأُ فِي يَوْمِنَا هَذَا أَنْ نُصَلِّيَ، ثُمَّ نَرْجِعَ فَنَنْحَرَ، فَمَنْ فَعَلَ ذَلِكَ فَقَدْ أَصَابَ سُنَّتَنَا، وَمَنْ نَحَرَ قَبْلَ الصَّلاَةِ فَإِنَّمَا هُوَ لَحْمٌ قَدَّمَهُ لأَهْلِهِ، لَيْسَ مِنَ النُّسْكِ فِي شَىْءٍ ‏"‏‏.‏ فَقَالَ رَجُلٌ مِنَ الأَنْصَارِ يُقَالُ لَهُ أَبُو بُرْدَةَ بْنُ نِيَارٍ يَا رَسُولَ اللَّهِ، ذَبَحْتُ وَعِنْدِي جَذَعَةٌ خَيْرٌ مِنْ مُسِنَّةٍ‏.‏ فَقَالَ ‏"‏ اجْعَلْهُ مَكَانَهُ، وَلَنْ تُوفِيَ أَوْ تَجْزِيَ عَنْ أَحَدٍ بَعْدَكَ ‏"‏‏

Narrated By Al-Bara' bin 'Azib : 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 Apostle! I slaughtered the Nusuk (before the prayer) but I have a young she-goat which is better than an older sheep." The Prophet I said, "Sacrifice it in lieu of the first, but it will be not sufficient (as a sacrifice) for anybody else after you."