Hawzah News Agency – Q: My mother is seriously sick, and my father is also physically weak. Nevertheless, both of them fast. Sometimes, it is quite evident that fasting aggravates their illness. So far, I have not been able to persuade them to refrain from fasting at least at times when their illness is serious. Please guide us concerning the rule that applies to their fasting?

A: The criterion in determining the inability to fast, or whether fasting causes illness, or aggravates it, is the opinion of the fasting person himself. However, if he knows that fasting is harmful for him and he still decides to fast, it is ḥarām.

Source: https://www.leader.ir/en/book/32/Practical-Laws-of-Islam