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.