Sahih Bukhari Volume 002, Book 015, Hadith Number 100.
Narated By Anas bin Malik : Allah's Apostle offered the prayer on the day of Nahr and then delivered the Khutba and ordered that whoever had slaughtered his sacrifice before the prayer should repeat it, that is, should slaughter another sacrifice. Then a person from the Ansar stood up and said, "O Allah's Apostle! because of my neighbors (he described them as being very needy or poor) I slaughtered before the prayer. I have a young she-goat which, in my opinion, is better than two sheep." The Prophet gave him the permission for slaughtering it as a sacrifice.