Question: What are the days, apart from Ramadaan, on which it is Mustahab (desirable) to observe Sawm (Fast)? What are the days on which it is not Mustahab to observe Sawm? Does it suffice a person to fast the month of Ramadaan only? Is observing Sawm in Ramadaan a Fareedah (obligatory act) or a Sunnah (supererogatory act of worship following the example of the Prophet)? Please clarify this with evidence from the Qur’aan and Sunnah.
Answer: Observing Sawm in Ramadaan is one of the five pillars of Islaam. The textual proof of its obligation is the Qur’aan, Sunnah, and Ijmaa` (consensus of scholars)… read more here.