If someone does something against his oath due to forgetfulness
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 ".
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."