Sahih Bukhari Volume 2, Book 13, Hadith 977

حَدَّثَنَا أَبُو نُعَيْمٍ، قَالَ حَدَّثَنَا مُحَمَّدُ بْنُ طَلْحَةَ، عَنْ زُبَيْدٍ، عَنِ الشَّعْبِيِّ، عَنِ الْبَرَاءِ، قَالَ خَرَجَ النَّبِيُّ صلى الله عليه وسلم يَوْمَ أَضْحًى إِلَى الْبَقِيعِ فَصَلَّى رَكْعَتَيْنِ، ثُمَّ أَقْبَلَ عَلَيْنَا بِوَجْهِهِ وَقَالَ ‏"‏ إِنَّ أَوَّلَ نُسُكِنَا فِي يَوْمِنَا هَذَا أَنْ نَبْدَأَ بِالصَّلاَةِ، ثُمَّ نَرْجِعَ فَنَنْحَرَ، فَمَنْ فَعَلَ ذَلِكَ فَقَدْ وَافَقَ سُنَّتَنَا، وَمَنْ ذَبَحَ قَبْلَ ذَلِكَ فَإِنَّمَا هُوَ شَىْءٌ عَجَّلَهُ لأَهْلِهِ، لَيْسَ مِنَ النُّسُكِ فِي شَىْءٍ ‏"‏‏.‏ فَقَامَ رَجُلٌ فَقَالَ يَا رَسُولَ اللَّهِ، إِنِّي ذَبَحْتُ وَعِنْدِي جَذَعَةٌ خَيْرٌ مِنْ مُسِنَّةٍ‏.‏ قَالَ ‏"‏ اذْبَحْهَا، وَلاَ تَفِي عَنْ أَحَدٍ بَعْدَكَ ‏"‏‏.

Narrated By Al-Bara' : The Prophet went towards Al-Baqi (the grave-yard at Medina) on the day of Id-ul-Adha and offered a two-Rakat prayer (of 'Id-ul-Adha) and then faced us and said, "On this day of ours, our first act of worship is the offering of prayer and then we will return and slaughter the sacrifice, and whoever does this concords with our Sunna; and whoever slaughtered his sacrifice before that (i.e. before the prayer) then that was a thing which he prepared earlier for his family and it would not be considered as a Nusuk (sacrifice.)" A man stood up and said, "O, Allah's Apostle! I slaughtered (the animal before the prayer) but I have a young she-goat which is better than an older sheep." The Prophet (p.b.u.h) said to him, "Slaughter it. But a similar sacrifice will not be sufficient for anybody else after you."