Why is an insane exempted from Fasting?
Our beloved Prophet Muhammad (saws) said, its mentioned in the Hadith of Tirmidhi, Hadith no. 1423 that
“The pen is lifted from 3 categories of people. A child till he reaches puberty, a person who is sleeping till he wakes up and a person who is insane till he becomes of sound mind”
So this the Prophet has exempted and they are free from fasting, the reason is because one of the criteria for the fasting to be accepted is your Neeya, is intention. And intention can only be made by a person who is sane, of sound in mind, only if he is sound can he willingly intend to fast if he is insane, he cannot. So that’s the reason if an insane person whether he fasts or not it doesn’t make a difference at all. It is, he is exempted. And once he becomes sane he does not have to compensate also for the fast he has missed because he is not responsible for that, he is not held responsible. So that’s the beauty of Islam, they only held responsible those people who should be held responsible.