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
← Previous Hadith "I heard Ibn 'Umar say" "The Prophet used to fast three days of each month.

Sunan an-Nasa'i Book 22, Hadith 324 Next Hadith → "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