Majority of the scholars agree that this is a sinful act and that he should
b) make up for the missed days
c) pay kaffara ($7 to feed one person per each day missed).
Their evidence is the actions of the sahaba, such as Abu Huraira and ibn ‘Abbas.
Minority of the scholars say that the person only needs to repent and make up the days without having to pay kaffara. Their evidence is that there is no specific text that mentions that this act of worship (kaffara) applies in this case, and that the companions who did use to pay the kaffara did it out of abundance of caution.
In summary, if a person is not able to pay kaffara, then making up the days only is sufficient. However, if a person is able to pay the kaffara, then it is best to do so to be on the safe side and follow the opinion of the majority of the scholars