Al-Aswad heard Jundub (may Allah be pleased with him) say: I was present with the Prophet (peace and blessings be upon him) on the day of Eid al-Adha. He (peace and blessings be upon him) delivered a sermon: "Whoever slaughtered before the prayer, let him sacrifice another animal in place of the one he slaughtered, and whoever has not slaughtered, let him slaughter with the name of Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة العيدين / 6264