I have often heard that if someone fasts the six days of Shawwâl in a given year, then it becomes obligatory for that person to do so every year thereafter. Is this true?
There can be no doubt that we are encouraged to observe the six days of Shawwâl every year, simply because of the great reward we can receive by observing this fast.
Abû Ayyûb al-Ansârî relates that Allah's Messenger (peace be upon him) says: "Whoever fasts the month of Ramadan and then follows it with six days of fasting in the month of Shawwâl, it will be as if he had fasted the year through." [Sahîh Muslim (1163)]
Many people have this misconception that once a person observes the six days of Shawwâl, it becomes a permanent religious obligation for the person to fast those six days every year. This is simply not true.
The fast of Shawwâl is a voluntary fast, and all the legal rulings relating to offering a voluntary fast apply to it.
The Prophet (peace be upon him) said: "A person observing a voluntary fast is in charge of himself. If he wishes to fast, he may do so. If he wishes to break his fast, he may do so." [Sunan al-Tirmidhî (732)]
And Allah knows best.
Source: Islam Today
-- Al Arabiya Digital