What must be done by a Muslim who is ill and cannot fast in Ramadan?

Fasting Ramadan is a duty for every Muslim who has reached the age of accountability, is of sound mind, and a resident. In Islamic law, obligations are dependent on ability and capability. Therefore, when one is unable to fast or experiences an overwhelming difficulty, it is permissible to refrain from fasting for Allah Almighty says, “Allah does not charge a soul except [with that within] its capacity” (Quran, 2:286). The Prophet (peace and blessings be upon him) said, “If I forbid you from doing something, avoid it; and if I command you to do something, do as much of it as you are able” (Bukhari and Muslim). Moreover, Allah Almighty says, “So whoever among you is ill or on a journey [during them] - then an equal number of days [are to be made up]” (Quran, 2:184). This means that it is permissible for a Muslim who suffers from a recoverable illness and for a traveler to refrain from fasting, if they cannot fast, and to make it up once they are able.

In the case of a Muslim who suffers from an incurable illness that makes fasting impossible, or an old person who cannot bear the hardship of fasting, fasting is not obligatory. However, they are to pay fidya (compensation) which consists of feeding a poor person for every missed fast day of Ramadan. The fidya is measured as one mudd of the local staple food. According to the Hanafis, one mudd is equal to two Iraqi pounds (i.e., 812.5 grams), while according to the majority of scholars, it is equal to one and one-third Iraqi mudd (i.e., 510 grams), the latter being the opinion adopted for the fatwa. Moreover, it is not only permissible to pay the monetary equivalent of the fidya, but preferable as it is more beneficial to the poor and better fulfills their needs. If such a person later regains the ability to fast, they are not required to make up their missed fast days because they were initially required to pay fidya due to their circumstances.

And Allah Almighty knows best.