Sayyiduna Imran bin Husain (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said to him, or perhaps to another person: Have you fasted any days from the end of this month? He replied: No. The Prophet (peace and blessings be upon him) said: When you do not fast (any voluntary fasts) in a month, then fast one or two days.
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3587
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «صحيح أبي داود» (2016): قفضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح