Fasting six Days in the Month of Shawwal

Abu Ayyub (May Allah be pleased with him) reported:

The Messenger of Allah (Sallallahu Alaihi Wasallam) said,

"He who observes As-Saum (the fasts) in the month of Ramadan,

and also observes As-Saum for six days in the month of Shawwal,

it is as if he has observed As-Saum for the whole year."

(Muslim).