Is a Muslim permitted to break a voluntary fast due to a stomach illness?

One who observes a supererogatory fast is the master of his own will; if he wishes, he fasts, and if he wishes, he breaks his fast. However, it is recommended that he not break his fast without an excuse. As for the sick person who is harmed by fasting, there is no blame upon him for breaking his fast. He should make up the obligatory fast after recovery, for Allah Almighty says: "But whoever among you is ill or on a journey, then [he is to fast] an equal number of other days." A supererogatory fast is not made up.