"I heard the Messenger of Allah say: 'It is a good fast to fast three days of each month".
Sunan an-Nasa'i Book 22, Hadith 322
← Previous Hadith "I heard the Messenger of Allah say: "Whoever fasts three days of each month has fasted the month in full' or 'will have (the reward of) fasting the month."' 'Asim was in doubt.

Sunan an-Nasa'i Book 22, Hadith 321 Next Hadith → "Uthman bin Abi Al-As" and he narrated something similar in Mursal form.

Sunan an-Nasa'i Book 22, Hadith 323