Was too weak to fast

Q 11: My grandfather died without making up for the days that he did not fast during Ramadan due to his illness. I wanted to fast these days on his behalf, but I have to make up for some days missed during my menstruation. Am I permitted to fast on his behalf while I have to make up for my own missed days, or should I finish my missed days then offer Sawm on his behalf?

A: A person should hasten to make up for the missed days of Ramadan for himself first, then it is permissible to fast on behalf of any relative of his or hers as prescribed.If your grandfather died in a state of illness, then there is no need to make up for his missed days, but if he had recovered from this illness and lived a sufficient period to make up for the missed days, but did not fast these days, then you are entitled to offer Sawm on his behalf, for the prophet (peace be upon him) said: If anyone dies in a state (that he had to complete) some days of fast, his heir must fast on his behalf. The waliy here is the relative.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.