The Prophet ﷺ said regarding fasting three days of each month, "It is like fasting and breaking the fast of an entire lifetime."In another wording, "Fasting three days of every month is like fasting an entire lifetime and standing it in prayer."
قال النبي ﷺ في صيام ثلاثة أيام من الشهر: صوم الدهر، وإفطاره. وفي لفظ: صوم ثلاثة أيام من كل شهر صيام الدهر وقيامه.
Imam Ahmad narrated it (15584) from Affan, who said, Shuba narrated to us, from Muawiya bin Qurra, from his father, from the Prophet ﷺ, and he mentioned the hadith with the first wording. Bazzar likewise narrated it, in Kashf Astar (1059), through two routes, Muhammad bin Jafar and Yahya bin Saeed Qattan, both of them from Shuba with this wording. Waki also narrated it from Shuba, and Imam Ahmad narrated it (15594) through his route. Ibn Hibban narrated it (3652) from Abu Yaala, who said, Ubaydullah bin Umar Qawariri narrated to us, who said, Yahya bin Saeed narrated to us, from Shuba, from Muawiya bin Qurra, from his father, who said, and he mentioned it with the second wording.So it appears that the narrators differed regarding Yahya bin Saeed, or that he himself narrated it with both wordings. Affan, Waki, and Muhammad bin Jafar narrated it with the first wording. So Ibn Hibban's statement, "Waki's statement from Shuba in this report is 'his breaking of the fast,' while Yahya Qattan's statement from Shuba is 'and his standing in prayer,' and both of them are precise and reliable memorizers," is open to question, because Yahya bin Saeed Qattan narrated it with both wordings.The meaning of his statement, "Fasting three days of the month is like fasting a whole lifetime," is that a good deed is multiplied tenfold. And his statement, "and his breaking of the fast," means breaking the fast for a whole lifetime, for by fasting three days and then enjoying the remaining days by breaking the fast, it is as though he enjoyed breaking the fast for his entire lifetime.