Allaah’s Messenger(sall Allaah 3layhi wasSallam) said: “Whoever observes the Ramadhaan fast and follows it with six days in Shawwal, it is as if he has fasted the whole year.” [Al-Bukhari]

**(the word “dahr” is used, which some say might also mean lifetime instead of just year)

The Prophet (peace and blessings of Allaah be upon him) explained this when he said: “Whoever fasts for six days after (Eid) al-Fitr has completed the year: (whoever does a good deed (hasanah) will have ten hasanah like it).

”According to another report: “Allaah has made for each hasanah ten like it, so a month is like fasting ten months, and fasting six days completes the year.” (al-Nisaa’i and Ibn Maajah. See also Saheeh al-Targheeb wa’l-Tarheeb, 1/421).

It was also narrated by Ibn Khuzaymah with the wording: “Fasting for the month of Ramadaan brings the reward of ten like it, and fasting for six days brings the reward of two months, and that is the fasting of the whole year.”