Sahih Muslim
Sahih Muslim Book 022, Hadith Number 4821.
Hadith Section/Book: Sahih Muslim Sahih Muslim Book 22. Sacrifices
Chapter : The proper time for sacrifice.
Jundab al-Bajali reported: I saw Allah's Messenger (may peace be upon him) observing ('Id) prayer on the Day of Sacrifice (10th of Dhu'l-Hijja) and then delivering a sermon and he said: He who sacrificed the (animal) before offering ('Id) prayer, he should offer again in its stead, and he who did not sacrifice the animal should slaughter it by reciting the name of Allah.