Fasting According To the Five Schools of Islamic Law

Reprehensible (Makruh) Fasts

It is mentioned in al-Fiqh `ala al-madhahib al-'arba`ah that it is makruh to single out Fridays and Saturdays for fasting. So is fasting on the day of Now Ruz (21st March) in the opinion of all the schools except the Shafi`i, and fasting on the day or the two days just before the month of Ramadan.

It has been stated in Imami books on fiqh that it is makruh for a guest to fast without the permission of his host, for a child to fast without the permission of its father, and when there is doubt regarding the new moon of Dhu al-Hijjah and the consequent possibility of the day being that of `Id.