Abu Ayyub al-Ansari relates that the Prophet (peace be upon him) says:
Whoever fasts the month of Ramadan and then follows it with six days of fasting in the month of Shawwal, it will be as if he had fasted the year through. (Muslim)
The month of Shawwal is singled out for the observance of extra fasts, since this month follows immediately after Ramadan. The six days of voluntary fasting are to the obligatory fast of Ramadan what the Sunnah prayers are to the obligatory prayers.
It is related from Thawban that the Prophet (peace be upon him) said:
The fast of Ramadan is like observing ten months of fasting. Fasting six days of Shawwal is like observing two months of fasting. This together is like fasting throughout the year. (Sahih Ibn Khuzaymah (2115) and Sunan al-Nasa’i al-Kubra (2860))
Al-Nawawi observes (Sharh Sahih Muslim (8/56)):
Scholars have explained that it is like observing a year of fasting because the reward of a good deed is multiplied tenfold. Therefore fasting the month of Ramadan is like fasting for ten months and fasting six days in the month of Shawwal is like fasting for two months.
Virtues of Fasting Six Days in Shawwal
1. The Reward
Fasting six days in Shawwal after observing the Ramadan fast gives the person the reward of fasting throughout the year.
2. Covers up Deficiencies
The fasts of Sha’ban and Shawwal are like the Sunnah prayers that accompany the five obligatory prayers. Like the Sunnah prayers, these extra fasts cover up for the deficiencies in our performance of our obligatory worship.
On the Day of Judgment, our voluntary acts of worship will compensate for the shortcomings in how we carried out our duties. Most of us have deficiencies in our observance of our Ramadan fasts. We need something to cover up for those deficiencies.
[Note: The deficiencies being discussed here are not missing days of fasting. Rather, they are the deficiencies in our conduct that detract from the value of our worship.]
3. A Sign of Accepted Ramadan
Our return to the habit of fasting right after Ramadan, in Shawwal, is a sign of acceptance of our Ramadan fasts. When Allah accepts our worship, He blesses us to engage in further acts of piety.
The saying goes: “The reward of virtue is further virtue”.
Therefore, following one good deed with others like it is a sign that the first deed had been accepted by Allah.
Those who observe the fast of Ramadan get their recompense of the day of Eid al-Fitr. Getting into the habit of fasting again soon thereafter is a means of giving thanks to Allah for the blessings that we have received. There is no blessing greater than forgiveness of sins.
Indeed, Allah has commanded us to give thanks for the blessings of the Ramadan fast and to do so by making mention of Him and through other means of giving thanks. Allah says:
(He wants you) to complete the number of days, and to glorify Him in that He has guided you; and perchance you may give thanks. (2: 185)
Fasting these days in Shawwal is one way for us to express our thanks for Allah blessing us in our observance of the Ramadan fast.
It is known that some of the Pious Predecessors would try to get up at night to pray the Tahajjud prayer. When Allah blessed them to wake up and do so, they would fast the next day in thanks to Allah for blessing them to observe that prayer.
Once Wuhayb ibn al-Ward was asked about the blessings of various acts of devotion and he replied:
“Do not ask about the blessings that can be earned by performing these acts of worship. Rather, ask how you can show your thanks to Allah if He blesses you to perform them, for he is the one who assists us in doing so.”
Every blessing that Allah gives us is something that we have to be thankful about. Moreover, when Allah blesses us to show thanks, this is a further blessing from Allah that deserves further thanks from us. If we show further thanks, this in turn is another blessing deserving our gratitude.
There is no end to this. When we recognize that our thanks are never enough, this is the highest expression of gratitude we can give.
How We Should Fast the Six Days in Shawwal
There are various opinions about this question:
1. Some scholars hold the view to fast the six days in consecutive order, starting from the second day of Shawwal. This is the view of al-Shafi`i and Ibn al-Mubarak.
2. Others are of the opinion that it is preferable to fast the six days intermittently, spreading them out throughout the month of Shawwal. This is the position of Ahmad b. Hanbal and Waki`.
3. Then there are those who hold the view that the days should all be postponed until later in the month and not close to the day of `Eid, which is a time of celebration and feasting. They prefer fasting the three days in the middle of the month (ayyam al-bid) along with the three days right before or after. This is the opinion of Ma`mar and `Abd al-Razzaq.
There is considerable flexibility in all of this. We can choose to follow any of these approaches that we wish.
And Allah knows best.
Source: Islam Today.