Is it permissible to combine the intention of making up missed fasts with the intention of observing voluntary fasts?

It is not permissible to combine obligatory and voluntary fasting with a single intention, for each of them is an independent, intended act of worship. Combining two intended acts of worship is not permissible, unlike when one of them is not intended in itself, or when the combination is in the means. In the case of combining obligatory and voluntary [fasting], jurists have differed regarding the validity of the compensatory fast, or the voluntary fast, or the invalidity of both. Therefore, it is necessary to specify the intention for the obligatory fast alone to clear one's obligation, as this is the most cautious and preferred approach.