It is narrated from Sayyidah Hafsah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), that the Prophet (peace and blessings be upon him) used to fast three days of the month: Monday, Thursday, and the Monday of the following week.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19656
It is narrated from Sayyidah Hafsah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) used to fast Monday, Thursday, and the Monday of the following week.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19657