Abu Ayyub al-Ansari reported that the Prophet, upon whom be peace, said: "Whoever fasts during the month of Ramadan and then follows it with six days of Shawwal will be [rewarded] as if he had fasted the
entire year." This is related by "the group," except for al-Bukhari and anNasa'i.
According to Ahmad, one may fast on these days consecutively or nonconsecutive, as neither practice is preferred over the other.
Hanafiyyah and Shaf'iyyah maintain that it is preferable to fast on consecutive days after the 'Eid.