The Messenger of Allah ﷺ used to fast on the nine days of Dhul-Hijjah, the day of Ashura, and three days of every month, the first Monday of the month and Thursday.
حدثنا مسدد حدثنا أبو عوانة عن الحر بن الصباح عن هنيدة بن خالد عن امرأته
كان رسول الله ﷺ يصوم تسع ذي الحجة ويوم عاشوراء وثلاثة أيام من كل شهر أول اثنين من الشهر والخميس
Takhrij, its isnad is sahih. Nasai narrated it in the Book of Fasting, the chapter on the fasting of the Prophet ﷺ, may my father and mother be sacrificed for him, and the mention of the differences among the transmitters of the report on that matter, hadith no. 2374, from the hadith of Abu Awana, with the same wording.Hunaidah was a companion, and his wife was also a companion.