Is it permissible to change the intention of a make-up fast (qaḍāʾ) to a voluntary fast (taṭawwuʿ) after doubting the intention of the make-up fast before Fajr, and what are the implications if it is not permissible?

If a responsible individual (mukallaf) doubts their intention to fast for a make-up (qada’) fast before dawn, the default is that there was no intention, unless they suffer from obsessive doubts (waswas). In the latter case, they should proceed with their fast on the intention of make-up, because excessive doubts are not taken into consideration.

Whoever begins an obligatory fast, such as making up for Ramadan, is not permitted to break it except for a valid excuse. If they break it – whether with or without an excuse – they must make up that day without expiation (kaffarah).

If a Muslim changes their intention from a make-up fast to a supererogatory (nafl) fast, there is no expiation for them, but they must seek forgiveness and repent.

In summary, if the intention for a make-up fast was definitively made overnight, it is not permissible to break it. However, if it was actually broken, the Muslim must seek forgiveness and repent, and make up the day. If the doubt regarding making the intention overnight is considered valid, the default is that the intention was not made overnight, and the fast is valid as a supererogatory fast. But if the doubt is due to obsessive whispers (waswas), it does not affect the obligatory fast, and it is not permissible to break it.