Question: My father died and did not fast Ramadaan due to illness? Should I fast to make up for the missed days or provide needy people with food on his behalf? Which one is better?
Answer: If your father was able to make up for these missed days and did not do so, it is permissible for you to fast on his behalf. The Prophet (peace be upon him) stated: Whoever dies not having completed some days of the fast, an heir must fast on their behalf. (Agreed upon by Al-Bukhaaree and Muslim and reported by `Aa’ishah [may Allaah be pleased with her])... read more here.