What is the Islamic law about someone who breaks his fast thinking it is not obligatory on him to fast?

Answer

If he was certain that fasting is not obligatory on him, there is no kaffara on him nor is any fidya payable. However, Qadha is obligatory on him but if he was not certain about fasting not being obligatory, he should give both Qadha and kaffara. The kaffara is to feed sixty poor Shia Muslims by one mudd (750 grams) of foodstuffs to each 60 different needy Shia Muslims. Qadha should be performed in the same year and if it is delayed until the next Ramadhan, he should give the Qadha and kaffara of 750 grams of food stuffs for each day to the poor. If the Qadha is delayed again in the following years, the kaffara is not repeated.