Narrated Al Bara: The Prophet (peace be upon him) said (on the day of Id-al-Adha), “The first thing we will do on this day of ours, is to offer the (‘Id) prayer and then return to slaughter the sacrifice. Whoever does so, he acted according to our Sunna (tradition), and whoever slaughtered (the sacrifice) before the prayer, what he offered was just meat he presented to his family, and that will not be considered as Nusak (sacrifice).” (On hearing that) Abu Burda bin Niyar got up, for he had slaughtered the sacrifice before the prayer, and said, “I have got a six month old ram.” The Prophet (peace be upon him)said, ‘Slaughter it (as a sacrifice) but it will not be sufficient for any-one else (as a sacrifice after you).” Al-Bara’ added: The Prophet (peace be upon him)said, “Whoever slaughtered (the sacrifice) after the prayer, he slaughtered it at the right time and followed the tradition of the Muslims.”
Sahih Al-Bukhari – Book 68 Hadith 453

Narrated Anas bin Malik: The Prophet (peace be upon him) 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.”
Sahih Al-Bukhari – Book 68 Hadith 454

Narrated Uqba bin Amir: That The Prophet (peace be upon him) gave him some sheep to distribute among his companions to slaughter as sacrifices (‘Id-al-Adha). A kid was left and he told The Prophet (peace be upon him)of that whereupon he said to him, “Slaughter it as a sacrifice (on your behalf).”
Sahih Al-Bukhari – Book 68 Hadith 462

Narrated Anas: The Prophet (peace be upon him) slaughtered two rams, black and white in color (as sacrifices), and I saw him putting his foot on their sides and mentioning Allah’s Name and Takbir (Allahu Akbar). Then he slaughtered them with his own hands.
Sahih Al-Bukhari – Book 68 Hadith 465