The Prophet ﷺ said, "Whoever slaughtered the sacrifice before the prayer, he just slaughtered it for himself, and whoever slaughtered it after the prayer, he slaughtered it at the right time and followed the tradition of the Muslims."  

قَالَ النَّبِيُّ ﷺ مَنْ ذَبَحَ قَبْلَ الصَّلاَةِ فَإِنَّمَا ذَبَحَ لِنَفْسِهِ وَمَنْ ذَبَحَ بَعْدَ الصَّلاَةِ فَقَدْ تَمَّ نُسُكُهُ وَأَصَابَ سُنَّةَ الْمُسْلِمِينَ  

An uncle of mine called Abu Burda, slaughtered his sacrifice before the ʿId prayer. So Messenger of Allah ﷺ said to him, "Your (slaughtered) sheep was just mutton (not a sacrifice)." Abu Burda said, "O Allah's Apostle! I have got a domestic kid goat." The Prophet ﷺ said, "Slaughter it (as a sacrifice) but it will not be permissible for anybody other than you" The Prophet ﷺ added, "Whoever slaughtered his sacrifice before the (ʿId) prayer, he only slaughtered for himself, and whoever slaughtered it after the prayer, he offered his sacrifice properly and followed the tradition of the Muslims."  

لَهُ رَسُولُ اللَّهِ ﷺ شَاتُكَ شَاةُ لَحْمٍ فَقَالَ يَا رَسُولَ اللَّهِ إِنَّ عِنْدِي دَاجِنًا جَذَعَةً مِنَ الْمَعَزِ قَالَ اذْبَحْهَا وَلَنْ تَصْلُحَ لِغَيْرِكَ ثُمَّ قَالَ مَنْ ذَبَحَ قَبْلَ الصَّلاَةِ فَإِنَّمَا يَذْبَحُ لِنَفْسِهِ وَمَنْ ذَبَحَ بَعْدَ الصَّلاَةِ فَقَدْ تَمَّ نُسُكُهُ وَأَصَابَ سُنَّةَ الْمُسْلِمِينَ  

My maternal uncle Abu Burda sacrificed his animal before ('Id) prayer. Thereupon Messenger of Allah ﷺ said: That is a goat (slaughtered for the sake of) flesh (and not as a sacrifice on the day of Adha). He said: I have a lamb of six months. Thereupon he said: Offer it as a sacrifice, but it will not justify for anyone except you, and then said: He who sacrificed (the animal) before ('Id) prayer, he in fact slaughtered it for his own self, and he who slaughtered after prayer, his ritual of sacrifice became complete and he in fact observed the religious practice of the Muslims.  

ضَحَّى خَالِي أَبُو بُرْدَةَ قَبْلَ الصَّلاَةِ فَقَالَ رَسُولُ اللَّهِ ﷺ تِلْكَ شَاةُ لَحْمٍ فَقَالَ يَا رَسُولَ اللَّهِ إِنَّ عِنْدِي جَذَعَةً مِنَ الْمَعْزِ فَقَالَ ضَحِّ بِهَا وَلاَ تَصْلُحُ لِغَيْرِكَ ثُمَّ قَالَ مَنْ ضَحَّى قَبْلَ الصَّلاَةِ فَإِنَّمَا ذَبَحَ لِنَفْسِهِ وَمَنْ ذَبَحَ بَعْدَ الصَّلاَةِ فَقَدْ تَمَّ نُسُكُهُ وَأَصَابَ سُنَّةَ الْمُسْلِمِينَ  

"مَنْ ذَبَحَ بَعْدَ الصَّلاةِ تَمَّ نُسُكُه وَأَصَابَ سُنَّةَ الْمُسْلِمِينَ".  

"مَنْ ذَبَحَ قَبْلَ الصَّلاةِ فَإِنَّمَا يَذْبَحُ لِنَفْسِهِ، وَمَنْ ذَبَحَ بَعْدَ الصَّلاةِ فَقَدْ تَمَّ نُسُكُهُ، وَأَصَابَ سُنَّةَ الْمُسْلِمِينَ".