Language:
كتاب الأيمان والنذور
83  
Oaths and Vows
(15)
Chapter: If someone does something against his oath due to forgetfulness
(15)
بَابُ إِذَا حَنِثَ نَاسِيًا فِي الأَيْمَانِ
Sahih al-Bukhari 6674

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."

حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، حَدَّثَنَا شُعْبَةُ، عَنِ الأَسْوَدِ بْنِ قَيْسٍ، قَالَ سَمِعْتُ جُنْدَبًا، قَالَ شَهِدْتُ النَّبِيَّ صلى الله عليه وسلم صَلَّى يَوْمَ عِيدٍ ثُمَّ خَطَبَ ثُمَّ قَالَ ‏ "‏ مَنْ ذَبَحَ فَلْيُبَدِّلْ مَكَانَهَا، وَمَنْ لَمْ يَكُنْ ذَبَحَ فَلْيَذْبَحْ بِاسْمِ اللَّهِ ‏"‏‏.‏
Reference : Sahih al-Bukhari 6674
In-book reference : Book 83, Hadith 52
USC-MSA web (English) reference : Vol. 8, Book 78, Hadith 666
  (deprecated numbering scheme)