What is the obligatoy fasting?
There are three types of fasts that are obligatory:
a. Fasting in the Month of Ramadan
This is obligatory fasting because of the time itself. Fasting in the month of Ramadan is obligatory upon all Muslims who carry the conditions of being a mukallaf. In other words, Muslims who are able-minded, have reached puberty and have no valid excuse/impediment that will prevent them from fasting, are required to fast in the month of Ramadan.
The month of Ramadan, if the weather is clear, begins by the sighting of the crescent or by completing the month of Shaban with thirty days. In this regard, Allah’s Messenger said, “Start fasting on seeing the crescent (of Ramadan), and give up fasting on seeing the crescent (of Shawwal), and if the sky is overcast (and you cannot see it), complete Shaban to thirty days.”
If there has been a confirmed sighting of the new moon in a particular location, people residing in nearby areas in all directions must also fast based on this confirmed sighting. As for the meaning of ‘nearby’, it is defined as the two locations’ being less than 24 parasangs (72 miles or 133 km) away from each other. As for those who live in areas which are more distant, they are not required to fast based on the aforementioned sighting due to their disparate locations. This distance is applicable not to the countries that are on the same meridian but the ones which are in different meridians. This is because sighting of the crescent takes place at the same time in countries that are on the same meridian.
b. The Qada and Kaffarah (Atonement) of the Ramadan Fast:
It is an obligatory fast due to a specific reason. Making up the Ramadan fast that could not be performed or that was broken due to a valid excuse or without an excuse is an obligation.
The qada and kaffarah of the Ramadan fasts are listed under the group of the obligatory fasts which do not have specified days. According to most Muslim jurists making up and expiation of these fasts need to be fulfilled during the same year that they were missed.
Those who did not fast in the month of Ramadan must make up for these days during days other than the days during the month of Ramadan; the exception for this rule is the days when fasting is not allowed. As for the expiation fasting, it should be fulfilled for two hijri months or sixty days consecutively at a time when it is permissible to fast.
One must also fast for certain days as an atonement for various reasons such as breaking a vow, killing a person unintentionally, and making zihar (injurious comparison between one’s wife and one’s mother).
c. The Fast As a Fulfillment of a Vow (Nadhr):
This is the type of fasting which is made obligatory upon oneself through an oath. It is a fast vowed by a person to be fulfilled for the sake of Allah. This type of fasting has two types:
- Fasting vowed to be fulfilled without attaching to it a condition. If a day is specified for this type, it becomes obligatory to fast on that particular day and time. For example, if a person says:
“I promise to fast for the sake of Allah next Monday” it becomes obligatory for that person to fast on that specific Monday. If one vows to fast without specifying a day, e.g. if one says “I will fast one day for the sake of Allah”, it becomes obligatory to fast any day he/she chooses.
- The second type of votive fasting (nadhr) is the one attached to a condition. When the condition takes place, it becomes obligatory on the person to fast. For example, “If one says, such and such things happens I will fast three days for the sake of Allah, or if I retreat into seclusion in this mosque, I will fast for three days for the sake of Allah” it becomes obligatory for that person to fast when the conditions takes place.
 Al-Bukhari, Sawm, 5; al-Nasai, Siyam, 13
Source: Fiqh1 (According To The Shafi’i School Of Islamic Law), Erkam Publications