The ruling on fasting for one who finds out that the tenth day is not the one he fasted

Question: If a person fasted the ninth and the tenth, and then it became clear to him afterwards that he had actually fasted the eighth and the ninth, what is the ruling, and does he have to make up that fast?

Answer: He does not have to make it up, and he receives the full reward, if Allah wills, according to his intention; because he thought that this was the ninth and the tenth according to the calendars, so he gets his reward, if Allah wills, and he does not have to make it up, and he has the reward for fasting the two days.