What is the ruling for the ill in general? Is fasting, in their case, the default or a dispensation from Allah or vice versa?

Fasting is one of the obligatory duties of Islam which Allah Almighty prescribed based on one’s capacity to observe it. The principle regarding fasting, is that is an obligation for those who are able to perform it. If a Muslim is unable to abstain from food, drink, and other things that break the fast from dawn to sunset, one is permitted to take the dispensation of not fasting. Rather, if specialized doctors determine that fasting is harmful to one’s health, it is obligatory to refrain from fasting to preserve one’s health. Allah Almighty says, “Allah intends for you ease and does not intend for you hardship” (Quran, 2:185), “He has not placed upon you in the religion any difficulty” (Quran, 22:78), and “… and do not throw [yourselves] with your [own] hands into destruction” (Quran, 2:195).

Abu Huraira (may Allah be pleased with him) narrated that the Prophet (peace and blessings be upon him) said, “If I command you to do something, then do of it as much as you are able to” (recorded by Bukhari and Muslim). Therefore, if one is suddenly taken ill, one must make up one’s missed fast days. However, if the illness is persistent or ongoing, including chronic diseases and age-related ailments, there is no requirement to make up the missed fast days. Instead, what is required is fidya (compensation) which consists of feeding a needy person a mudd (0.75 kg) of food for each missed fast day.

And Allah Almighty knows best.