Is it the case that if someone began fasting as an expiation for an oath (kaffarat al-yameen) due to their inability to feed or clothe, and then acquired wealth during the fast, do they complete their fast or are they obligated to pay? And is it permissible to use the money from a charity box?

Whoever breaks an oath and begins fasting for its expiation, then becomes able to feed or clothe [the poor], it is permissible for him to complete his fasting, and his expiation will be considered sufficient according to the majority of scholars. And if he chooses to expiate by feeding or clothing, he may do so. If he begins fasting and then becomes able to free a slave, or feed, or clothe [the poor], he is not obliged to revert to those options, but if he wishes to move to the superior option, he may do so.