It is a condition for the validity of its performance to have the intention made at night, or an intention concurrent with the dawn; this is because this fasting is not specified, so the intention must be made until it is specified, as mentioned in the explanation of Al-Waqayah, p. 234, and in 'Umdat Al-Ri'ayah 1: 307. If he fasts with the intention after the dawn has risen, it will be considered a voluntary fast, and he must make up this voluntary fast if he invalidates it. However, if he thought he had to make up a day, and he started it with its conditions, then it became clear that he did not have to fast, he is not obligated to complete his fast nor to make it up; because he is excused due to forgetfulness, provided that he breaks his fast immediately. However, it is better to complete his fast. If he continues fasting after knowing that it is a make-up fast, he becomes obligated, and it is not permissible for him to break his fast. If he breaks the fast, he must make it up, as stated in Al-Hadiyah Al-'Ala'iyah, p. 156.