Lady Aisha Siddiqa (may Allah be pleased with her) narrates: During the blessed time of the Prophet Muhammad (peace be upon him), if any one of us (the noble wives) had missed fasts, she would not be able to make them up with the Prophet (peace be upon him) until the month of Sha'ban arrived. The reason for this was that the Prophet (peace be upon him) did not fast in any other month as much as he fasted in Sha'ban. He would not fast only a few days of it; otherwise, he would fast the entire month.
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3516
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الإرواء» (4/ 98): م.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده حسن