Sahih Bukhari Volume 009, Book 093, Hadith Number 497.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 93. Oneness, Uniqueness of Allah (Tawheed)
Narrated By Jundab : That he witnessed the Prophet on the Day of Nahr. The Prophet offered prayer and then delivered a sermon saying, "Whoever slaughtered his sacrifice before offering prayer, should slaughter another animal in place of the first; and whoever has not yet slaughtered any, should slaughter a sacrifice and mention Allah's Name while doing so."