Is a supererogatory fast, such as the fast of Ashura, to be made up if missed due to illness, or is it not permissible to make it up?

If you intended to fast on Ashura but were prevented by illness, you will receive the reward for fasting, based on the Prophet's (peace and blessings be upon him) saying: "If a servant falls ill or travels, what he used to do when he was a resident and healthy will be recorded for him." As for making up the day of Ashura, it is recommended according to some scholars, such as the Shafi'is, who consider it recommended to make up a regular fast if its time has passed.