Impermissibility of Observing Mustaḥab Fast for the One Who Has Qaḍa Fasts
Issue No. 1327- If a person has a qaḍā fast from the Holy month of Ramadan or another obligatory fast due on him to perform, it is not permissible for him to perform a recommended fast. In case he performs a recommended fast out of forgetfulness and remembers before ẓuhr, he can switch his intention to the obligatory fast. If however, one notices this after ẓuhr, his fast is void.
