What should a Muslim do who is unable to fast in Ramadan—due to illnesses that necessitate taking medication regularly during periods that prevent fasting—based on the advice of a non-Muslim doctor, and what is the expiation in this case, and is it permissible to pay it before the month, or after it, or in installments?

Scholars differ on the permissibility of acting upon the advice of a non-Muslim doctor. Ibn Uthaymeen, may Allah have mercy on him, was of the opinion that it is permissible to act upon his advice if his truthfulness and trustworthiness are known. He based this on the fact that the Prophet, peace and blessings be upon him, hired a trustworthy polytheist during the Hijra to guide him on the way.

If it is possible to consult a Muslim doctor, that is preferable. Otherwise, it is permissible to act upon the advice of a trustworthy non-Muslim doctor.

If breaking the fast is permissible due to illness, then it is obligatory to make up the number of days missed if the illness is curable. If the illness is incurable, then it is obligatory to feed a poor person for each day.