It is narrated from Sayyiduna Ali (may Allah be pleased with him) that a man came to the presence of the Messenger and said: O Messenger of Allah! Tell me of a month, besides Ramadan, in which I can fast. The Prophet (peace and blessings be upon him) said: "If you want to fast in any month after Ramadan, then fast in the month of Muharram, for it is the month of Allah. In it is a day on which Allah accepted the repentance of a people, and Allah will accept the repentance of a people."
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 1335
Hadith Gradingحکم دارالسلام:إسناد ضعيف لضعف عبدالرحمن بن إسحاق و لجهالة النعمان بن سعد