Imam Al-Nawawi’s Riyad-us-Saliheen
Chapter 228
The Desirability of Fasting six Days in the Month of Shawwal
1254. Abu Ayyub (May Allah be pleased with him) reported: The Messenger of Allah (sallallaahu alayhi wa sallam) said, “He who observes As-Saum (the fasts) in the month of Ramadan, and also observes As-Saum for six days in the month of Shawwal, it is as if he has observed As-Saum for the whole year.”
[Muslim].
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