The Messenger of Allah ﷺ said, "Whoever fasts six days after Eid al-Fitr has completed the year, 'Whoever brings a good deed shall have ten times its like' [Anam 6:160]."
حدثنا هشام بن عمار حدثنا بقية حدثنا صدقة بن خالد حدثنا يحيى بن الحارث الذماري قال سمعت أبا أسماء الرحبي
عن رسول الله ﷺ أنه قال من صام ستة أيام بعد الفطر كان تمام السنة {من جاء بالحسنة فله عشر أمثالها}
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[Sahih]. Ahmad, Nasai in al-Kubra, and Bayhaqi (4/293) and others narrated it through routes from Yahya bin Harith with this wording, and Ibn Khuzayma declared it sahih, no. 2115, as did Ibn Hibban (al-Ihsan), vol. 3635. Mizzi mentioned in al-Atraf (2/138, 139) that Ibn Majah narrated it from Hisham bin Ammar, from Sadaqa bin Khalid, from Yahya, with this wording, but he did not mention Baqiyya. And Allah knows best.