Fasting the six days of Shawwal is not obligatory as holy month of Ramadhan but if a muslim wants to be taken as if he/she has fasted the whole year, then he/she should fast the six days of Shawwal. The six days (sittat Shawwal) can only be fasted in the month of Shawwal. In the Sahih Muslim: Book 006: Number 2614: Abu Ayyub al Ansari (May Allah be pleased with him) reported that Prophet Muhammad (SAW) said “He who observed the fast of Ramadhan and then followed it with six (fasts) of Shawwal, it would be as if he fasted perpetually (continuously)”, i.e, the whole year. It is highly recommended to fast six days in the month of Shawwal, as this is a meritorious act which results in abundant reward. While some scholars are of the opinion that these six days of fasting must be completed in a continuous order right after the end of Ramadhan, many others say it is not required to fast six days continuously without any interruption. According to the second group, one can fast in accordance with convenience any time during the month of Shawwal.The reward of a good deed is multiplied by 10.
“He who observed the fast of Ramadhan and then followed it with six (fasts) of Shawwal, it would be as if he fasted perpetually (continuously)”(Sahih Muslim)
Consider fasting in holy month of Ramadhan successfully as a good deed. This equals 10 months of fasting. Likewise, if a muslim fasts for six days in Shawwal (which is still one of the four sacred months) and multiply that by 10, it equals 60 days. Mathematically, 60 days (2 months) added to 10 months equals 12 months or one year. Another important benefit of fasting six days of Shawwaal is that is makes up for any shortfall in a person’s obligatory Ramadaan fasts, because no one is free of shortcomings or sins that have a negative effect on his fasting. Fasting poses a prospect for that special direct connection with the Creator- the Almighty Allah. Indeed, it is a worship that draws the believer closer to Allah and closer to perfection. And it is an opportunity to a healthier and longer life for it has been proved that fasting helps the body to eliminate toxins from its system. May Almighty Allah guide us to that which pleases Him, correct our faith and establish us firmly upon the true religion. Amin!