📖 Abu Ayyub RadhiAllahu 'anhu narrated: Allah's noble Messenger Muhammad SallAllahu 'alaihi wa sallam said, "Whoever fasts the month of Ramadan and then follows it with six days of fasting in the month of Shawwal, it will be as if he fasted for the entire year."
Source: Sahih Muslim 1164
Grade: Sahih (Authentic) according to Muslim