Yahya related to me from Malik from Suhayl ibn Abi Salih from his father from Abu Hurayra that the Messenger of Allah ﷺ said, "Whoever makes an oath and then sees that something else would be better than it, should do kaffara for his oath and do what is better."
Yahya said that he heard Malik say, "Anyone who says that he has a vow but does not mention the name of Allah, is still obliged to make the kaffara for an oath (if he breaks it)".
Malik said, "Emphasis is when a man swears one thing several times, repeating the oath in his speech time after time. For instance, the statement, 'By Allah, I will not decrease it from such-and-such,' sworn three times or more. The kaffara of that is like the kaffara of one oath. If a man swears, 'I will not eat this food or wear these clothes or enter this house,' that is all in one oath, and he is only obliged to do one kaffara. It is the same for a man who says to his wife, 'You are divorced if I clothe you in this garment or let you go to the mosque,' and it is one entire statement in the normal pattern of speech. If he breaks any of that oath, divorce is necessary, and there is no breaking of oath after that in whatever he does. There is only one oath to be broken in that."
Malik said, "What we do about a woman who makes a vow without her husband's permission is that she is allowed to do so and she must fulfill it, if it only concerns her own person and will not harm her husband. If, however, it will harm her husband, he may forbid her to fulfill it, but it remains an obligation against her until she has the opportunity to complete it."
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ سُهَيْلِ بْنِ أَبِي صَالِحٍ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ " مَنْ حَلَفَ بِيَمِينٍ فَرَأَى غَيْرَهَا خَيْرًا مِنْهَا فَلْيُكَفِّرْ عَنْ يَمِينِهِ وَلْيَفْعَلِ الَّذِي هُوَ خَيْرٌ " .