The Messenger of Allah ﷺ used to fast three days at the beginning of every month.
حدثنا أبو كامل حدثنا أبو داود حدثنا شيبان عن عاصم عن زر
كان رسول الله ﷺ يصوم يعني من غرة كل شهر ثلاثة أيام
[Its isnad is hasan] Tirmidhi narrated it, Fasting, chapter on what has been said about fasting on Friday, 742, from the hadith of Shayban, through the same route, and he said, "Hasan gharib."