What is the method for fasting on behalf of the deceased, its rulings, and is it permissible?

Fasting on behalf of the deceased is no different from fasting for the living, and it is divided into categories: that which is unanimously not required and that which is disputed.

Unanimously Not Required: If the deceased broke their fast due to a legitimate Shar'i excuse and was unable to make up for it before dying, such as the excuse continuing until death or there being no time for atonement. Disputed Regarding Its Requirement: If the deceased had to make up for missed days of Ramadan or a vow fast and neglected to do so until death. Some scholars held that the guardian is obligated to fast on their behalf, based on the Hadith: "Whoever dies owing fasts, let his guardian fast on his behalf." While others forbade this. The preponderant view is that it is not obligatory for the guardian, but rather recommended, though there is a difference of opinion regarding the consensus on its non-obligation.