Fasting on the day which one believes to be the day of the Mi’raaj is not permissible, and comes under the heading of bid’ah. Even if a person is not sure, but he fasts this day for the sake of being on the safe side, it is as if he is saying, ‘If it is really the day of the Mi’raaj, then I will have fasted it, and if it is not, it will still be a good action that I have done, and if I will not be rewarded for it then I will not be punished.’ This attitude means that a person is committing bid’ah, and he is a sinner who deserves to be punished. But if his fast is not because it is the day of the Mi’raaj, but is rather because it is his habit to fast alternate days, or to fast Mondays and Thursdays, and that happens to coincide with the day known as the day of the Mi’raaj, there is nothing wrong with him fasting it with that intention, i.e., the intention of fasting on Monday or Thursday, or a day on which he usually fasts.