The Messenger of Allah ﷺ delivered a sermon to us on the day of sacrifice after the prayer. He said: If anyone prays like our prayer, and sacrifices like our sacrifice, his sacrifice is all right. If anyone sacrifices before the prayer (for 'Id), that is goat meant for flesh. Abu Burdah b. Niyar stood up and said: Messenger of Allah, I swear by Allah, I sacrificed before I went for prayer. I thought it was the day of eating and drinking; so I made haste, and ate myself, and supplied flesh to my family and neighbors. The Messenger of Allah ﷺ said: That is a goat meant for eating flesh. He said: I have a kid (of less than a year) which is better than two goats meant for flesh. Will it be valid from me ? He said: Yes, but it will not be valid for anyone after you. (Using translation from Abū Dāʾūd 2800)   

خَطَبَنَا رَسُولُ اللهِ ﷺ يَوْمَ النَّحْرِ بَعْدَ الصَّلَاةِ فَقَالَ مَنْ صَلَّى صَلَاتَنَا وَنَسَكَ نُسُكَنَا فَقَدْ أَصَابَ النُّسُكَ وَمَنْ نَسَكَ قَبْلَ الصَّلَاةِ فَتِلْكَ شَاةُ لَحْمٍ فَقَامَ أَبُو بُرْدَةَ بْنُ نِيَارٍ فَقَالَ يَا رَسُولَ اللهِ لَقَدْ نَسَكْتُ قَبْلَ أَنْ أَخْرُجَ إِلَى الصَّلَاةِ وَعَرَفْتُ أَنَّ الْيَوْمَ يَوْمُ أَكْلٍ وَشُرْبٍ فَتَعَجَّلْتُ فَأَكَلْتُ وَأَطْعَمْتُ أَهْلِي وَجِيرَانِي فَقَالَ رَسُولُ اللهِ ﷺ تِلْكَ شَاةُ لَحْمٍ قَالَ فَإِنَّ عِنْدِي عَنَاقَ جَذَعَةٍ هُوَ خَيْرٌ مِنْ شَاتَيْ لَحْمٍ فَهَلْ تَجْزِي عَنِّي؟ قَالَ نَعَمْ وَلَنْ تَجْزِيَ عَنْ أَحَدٍ بَعْدَكَ  

The Prophet ﷺ went towards Al-Baqi (the graveyard at Medina) on the day of Id-ul-Adha and offered a two-rakʿat prayer (of ʿId-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, Messenger of Allah ﷺ! I slaughtered (the animal before the prayer) but I have a young she-goat which is better than an older sheep." The Prophet ﷺ said to him, "Slaughter it. But a similar sacrifice will not be sufficient for anybody else after you." (Using translation from Bukhārī 976)   

خَرَجَ إِلَيْنَا رَسُولُ اللهِ ﷺ يَوْمَ أَضْحَى إِلَى الْبَقِيعِ فَقَامَ فَصَلَّى رَكْعَتَيْنِ ثُمَّ أَقْبَلَ عَلَيْنَا بِوَجْهِهِ فَقَالَ إِنَّ أَوَّلَ نُسُكِنَا فِي يَوْمِنَا هَذَا أَنْ نَبْدَأَ بِالصَّلَاةِ ثُمَّ نَرْجِعَ فَنَنْحَرَ فَمَنْ فَعَلَ ذَلِكَ فَقَدْ وَافَقَ سُنَّتَنَا وَمَنْ ذَبَحَ قَبْلَ ذَلِكَ فَإِنَّمَا هُوَ لَحْمٌ عَجَّلَهُ لِأَهْلِهِ لَيْسَ مِنَ النُّسُكِ فِي شَيْءٍ فَقَامَ خَالِي فَقَالَ يَا رَسُولَ اللهِ أَنَا ذَبَحْتُ وَعِنْدِي جَذَعَةٌ خَيْرٌ مِنْ مُسِنَّةٍ قَالَ اذْبَحْهَا ثُمَّ لَا تُوَفِّي جَذَعَةٌ بَعْدَكَ قَالَ زُبَيْدٌ فَسَمِعْتُ بَعْضَ أَصْحَابِنَا أَنَّهُ قَالَ عَنَاقُ جَذَعَةٍ  

[Machine] Junadab heard someone say, "I witnessed the Prophet ﷺ delivering a sermon on the day of Eid al-Adha. He said, 'Whoever slaughtered his sacrifice before the prayer should slaughter another in its place, and whoever has not yet slaughtered should slaughter one in the name of Allah.'" This narration is found in Sahih Hadith of Shu'bah.  

سَمِعَ جُنْدُبًا يَقُولُ شَهِدْتُ النَّبِيَّ ﷺ يَخْطُبُ يَوْمَ أَضْحَى فَقَالَ مَنْ كَانَ ذَبَحَ مِنْكُمْ قَبْلَ الصَّلَاةِ فَلْيُعِدْ مَكَانَ ذَبِيحَتِهِ أُخْرَى وَمَنْ لَمْ يَكُنْ ذَبَحَ فَلْيَذْبَحْ بِاسْمِ اللهِ أَخْرَجَاهُ فِي الصَّحِيحِ مِنْ حَدِيثِ شُعْبَةَ