My father died on the third day of Ramadan. Do I have to complete Ramadaan for him, i.e., should I fast on his behalf for twenty-seven days?.
You do not have to do anything, because when your father died, obligatory duties ceased for him, so you do not have to fast on his behalf, and it is not prescribed for you to do so. End quote.
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him)