Question 1: Is it permissible for someone to fast continuously day and night, for three days during the month of Ramadaan instead of fasting the whole month?
Answer: It is not permissible to do so and none of the scholars have ever said that it is permissible to do so, as night is not a time of fasting. Anyone who does so is in violation of Islaamic law, and has innovated a new legislation that was not ordained by Allaah. Additionally, they will be breaking their fast during the month of Ramadan without a legal excuse. Allaah (Glorified be He) made fasting the entire month of Ramadaan… read more here.