صَحِيحُ مُسْلِمٍ
Sahih Muslim 1651 c
The Book of Oaths
It is recommended for the one who swears an oath then sees that something else is better than it; To do that which is better and offer expiation for his oath
حَدَّثَنِي مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، وَمُحَمَّدُ بْنُ طَرِيفٍ الْبَجَلِيُّ، - وَاللَّفْظُ لاِبْنِ طَرِيفٍ - قَالاَ حَدَّثَنَا مُحَمَّدُ بْنُ فُضَيْلٍ، عَنِ الأَعْمَشِ، عَنْ عَبْدِ الْعَزِيزِ بْنِ رُفَيْعٍ، عَنْ تَمِيمٍ الطَّائِيِّ، عَنْ عَدِيٍّ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا حَلَفَ أَحَدُكُمْ عَلَى الْيَمِينِ فَرَأَى خَيْرًا مِنْهَا فَلْيُكَفِّرْهَا وَلْيَأْتِ الَّذِي هُوَ خَيْرٌ .
'Adi reported Allah's Messenger (ﷺ) as saying: When anyone amongst you takes an oath, but he finds (something) better than that he should expiate (the breaking of the oath), and do that which is better.
Sahih Muslim, 1651 cSahihصحيح