Sahih Muslim Book 22, Hadith Number 4819.

Chapter : The proper time for sacrifice.

Jundab b. Sufyan reported: I was with Allah’s Messenger (may peace be upon him) (on the occasion) of ‘Id al-Adha. After he had completed the prayer with people, he found that the goats had been slaughtered, whereupon he said: He who slaughtered sacrificial animal before the prayer should slaughter a goat (again) in its stead and he who has not slaughtered he should slaughter it by reciting the name of Allah.