It is narrated from Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Whoever fasts Ramadan and then follows it with six fasts of Shawwal, that is like perpetual fasting." The narrator said: I asked him: Is it ten days' reward for each day? He said: "Yes."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3887