What is the ruling on fasting expiatory days whose number and cause have been forgotten?

If a Muslim swears multiple oaths regarding different matters, he must offer expiation for each oath he breaks. However, if he swears repeated oaths concerning one matter and does not offer expiation, then a single expiation is due for all those oaths. The expiation for an oath is to feed ten poor persons, or clothe them, or free a slave. If one cannot find any of these, then he must fast for three days. If someone forgets the number of expiations due upon him, he should expiate for the number of oaths he is certain were binding upon him. If he doubts their number, he should expiate for what he believes will clear his conscience, just as if he had missed prayers, he should make them up until he is certain his responsibility is fulfilled.