"I entered upon the Mother of the Believers and heard her say: 'The Messenger of Allah used to fast three days of each month: The first Monday of the month, then Thursday, then the following Thursday."
Sunan an-Nasa'i Book 22, Hadith 326
← Previous Hadith the Messenger of Allah used to fast three days of each month: Monday at the beginning of the month, the following Thursday, then the Thursday after that.

Sunan an-Nasa'i Book 22, Hadith 325 Next Hadith → "There are four things which the Prophet never gave up: Fasting 'Ashura', (fasting during) the ten days, (fasting) three days of each month, and praying two Rak'ahs before Al-Ghadah (Fajr)."

Sunan an-Nasa'i Book 22, Hadith 327