Doubt concerning the number of divorces (talaaq)

If the husband is unsure as to whether he uttered the
word of divorce at all, or as to the number of divorces he has uttered,
then he should act on the basis of what is certain. So if he is not
sure whether he has divorced her or not, the basic principle is that
divorce has not taken place, because [in this instance] nikaah (marriage)
is something which is certain, and divorce is something concerning which
there is uncertainty. One of the basic principles is that certainty
cannot be overridden by doubt. If he is uncertain as to whether he has
divorced her once or twice, he should assume that he has divorced her
once, because this is what is certain.