Sunan an-Nasa'i 2417
سنن النسائي#2417SahihIt was narrated from Hunaidah bin Khalid, from his wife, from one of the wives of the Prophet, that:the Messenger of Allah used to fast nine days of Dhul-Hijjah, the day of 'Ashura', and three days of each month: The first Monday of the month, and two Thursday
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 22:328