Abu Dawud Book 9, Hadith Number 2794.

Narated By Al-Bara’ b. ‘Azib : The Apostle of Allah (PBUH) delivered a sermon to us on the day of sacrifice after the prayer. He said: If anyone prays like our prayer, and sacrifices like our sacrifice, his sacrifice is all right. If anyone sacrifices before the prayer (for ‘Id), that is a goat meant for flesh. Abu Burdah b. Niyar stood up and said: Apostle of Allah, I swear by Allah, I sacrificed before I went for prayer. I thought it was the day of eating and drinking; so I made haste, and ate myself, and supplied flesh to my family and neighbours. The Apostle of Allah (PBUH) said: This is a goat meant for eating flesh. He said: I have a kid (of less than a year) which is better than two goats meant for flesh. Will it be valid for me? He said: Yes, but it will not be valid for anyone after you.