1– Those for whom there is the hope of recovery, such as those with temporary sickness from which there is the hope of recovery. In this case the ruling is as Allah says (interpretation of the meaning): “But if any of you is ill or on a journey, the same number (should be made up) from other days.” [al-Baqarah 2:184]. All they have to do is wait until they are better, then fast. If it so happens that the sickness continues and the person dies before recovering, then there is no sin on him, because Allah has only enjoined him to make it up from other days, but he died before those other days came. This is like a person who dies in Sha’baan before Ramadaan begins – so it should not be made up on his behalf.
2– Cases where sickness is ongoing, such as cancer – Allah forbid – kidney disease, diabetes and similar chronic diseases where there is no hope of recovery. These people are allowed not to fast in Ramadaan, but they have to feed one poor person for each day, like old men and women who are unable to fast, so they may not fast and should feed one poor person for each day. The evidence for that in the Qur’aan is the verse in which Allah says (interpretation of the meaning): “And as for those who can fast with difficulty, (e.g. an old man), they have (a choice either to fast or) to feed a Miskeen (poor person) (for every day)” [al-Baqarah 2:184].