´It was narrated from Hunaidah bin Khalid that his wife said:` "One of the wives of the Prophet said: "The Prophet used to fast on the day of 'Ashura, nine days of Dhul-Hijjah and three days each month: The first Monday of the month, and two Thursday."
Hadith Referenceسنن نسائي / كتاب الصيام / 2374
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:إسناده صحيح