Question :
If someone fasts six days of Shawwaal, then one year he gets sick or something prevents him from fasting, or he is too lazy to fast, will there be any sin on him? We have heard that if a person fasts these six days one year, he must never give up this practice thereafter.

Answer :
Praise be to Allaah.
Fasting six days of Shawwaal after the day of Eid is Sunnah. It is not waajib (obligatory) on the person who does this once or more often to continue doing it. He is not guilty of a sin if he does not fast these days.
And Allaah is the Source of strength. May Allaah bless our Prophet Muhammad and grant him peace.

Fataawa al-Lajnah al-Daa�imah, 10/391