It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that I heard the Prophet (peace and blessings be upon him) say: Whoever fasts in the month of Ramadan and then follows it with six days of fasting in the month of Shawwal, it is as if he has fasted for the whole year.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 14477
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف كسابقه، وهو مكرر: 14302