Is expiation (kaffarah) obligatory for one who made vows but did not fulfill them on some days unintentionally, and how is this expiation to be performed if it is obligatory?

Doubt concerning the first two vows does not necessitate their fulfillment, due to the principle of the presumption of innocence (bara'at al-dhimma). As for the third vow, which is confirmed, it must be fulfilled according to the specified manner and time. It is not permissible to delay it except for an acceptable excuse. If it is delayed without an excuse, the seer (one who made the vow) incurs sin, and its fulfillment becomes obligatory as a make-up. The more probable opinion is that expiation is not obligatory for the delay.