Rabi’ah bin Ghaz reports: He asked Lady Aisha (may Allah be pleased with her) about the Prophet Muhammad (peace be upon him) observing (voluntary) fasting: So Lady Aisha (may Allah be pleased with her) replied: The Prophet Muhammad (peace be upon him) used to fast for almost the entire month of Sha’ban, to the extent that he would join it with Ramadan, but he would especially observe fasting on Mondays and Thursdays.
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3643
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «مختصر الشمائل» (258)، «الإرواء» (4/ 105 - 106)، «التعليق على «ابن خزيمة»» (2116).فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح