Sahih Muslim 1649e

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

وَحَدَّثَنِي عَلِيُّ بْنُ حُجْرٍ السَّعْدِيُّ وَإِسْحَاقُ بْنُ إِبْرَاهِيمَ وَابْنُ نُمَيْرٍ عَنْ إِسْمَاعِيلَ ابْنِ عُلَيَّةَ عَنْ أَيُّوبَ عَنِ الْقَاسِمِ التَّمِيمِيِّ عَنْ زَهْدَمٍ الْجَرْمِيِّ