(15) بَابُ إِذَا حَنِثَ نَاسِيًا فِي الأَيْمَانِ
Narrated Jundub:
I witnessed the Prophet (ﷺ) offering the `Id prayer (and after finishing it) he delivered a sermon and said, "Whoever has slaughtered his sacrifice (before the prayer) should make up for it (i.e. slaughter another animal) and whoever has not slaughtered his sacrifice yet, should slaughter it by mentioning Allah's Name over it."
Reference: Sahih al-Bukhari 6674
In-book reference: Book 83, Hadith 52
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 8, Book 78, Hadith 666