What is the ruling on one who had intercourse with his wife twice during the daytime in Ramadan, thinking that Fajr had not yet broken, and he did not exert effort to ascertain the timing?

A Muslim must ascertain the entry of the fasting time. Whoever has intercourse with his wife, thinking that night remains or doubting it, and then it becomes clear that he had intercourse during the day, is not required to offer expiation (kaffarah), but only to make up the fast (qada'). This is because he did not intend to violate the sanctity of the fast, and expiation is waived by doubt.