The Messenger of Allah ﷺ used to instruct us to fast the white days, the thirteenth, fourteenth, and fifteenth. He said, "They are like fasting the entire year."
حدثنا محمد بن كثير حدثنا همام عن أنس أخي محمد
كان رسول الله ﷺ يأمرنا أن نصوم البيض ثلاث عشرة وأربع عشرة وخمس عشرة قال وقال هن كهيئة الدهر
Grading, its chain is daif. Nasai transmitted it in the Book of Fasting, chapter on the difference of narrations attributed to Musa bin Talha regarding fasting three days of the month, hadith 2434, and Ibn Saad in Tabaqat, 7/43, from the hadith of Hammam through this same chain. Ibn Majah also narrated it, hadith 1707, and Ibn Hibban graded it sahih, hadith 1946.Abdul-Malik bin Qatada bin Milhan is mastur (of unknown reliability), and no one but Ibn Hibban declared him trustworthy.