One who swears an oath and then sees that something else is better Sunan Ibn Majah 2109
Arabic hadith text
حَدَّثَنَا مُحَمَّدُ بْنُ أَبِي عُمَرَ الْعَدَنِيُّ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، حَدَّثَنَا أَبُو الزَّعْرَاءِ، عَمْرُو بْنُ عَمْرٍو عَنْ عَمِّهِ أَبِي الأَحْوَصِ، عَوْفِ بْنِ مَالِكٍ الْجُشَمِيِّ عَنْ أَبِيهِ، قَالَ قُلْتُ يَا رَسُولَ اللَّهِ يَأْتِينِي ابْنُ عَمِّي فَأَحْلِفُ أَنْ لاَ، أُعْطِيَهُ وَلاَ أَصِلَهُ . قَالَ " كَفِّرْ عَنْ يَمِينِكَ "
Translation
It was narrated from Abul-Ahwas 'Awf bin Malik Al- Jushami that his father said
"I said: 'O Messenger of Allah, my cousin comes to me and I swear that I will not give him anything or uphold the ties of kinship with him.' He said: 'Offer expiation for what you swore about.'"