صحیح ابن حبان
Ibn Hibban
كتاب الصوم
Book of Fasting
باب صوم التطوع - ذكر تفضل الله بكتبة صيام الدهر وقيامه لمن صام الأيام الثلاثة من الشهر
Voluntary Fasting - Allah’s favor in granting the reward of perpetual fasting and night prayer to those who fast three days a month
1 hadith
Hadith 3652
Muawiyah bin Qurrah narrates from his father that the Prophet Muhammad (peace be upon him) said: "Fasting three days in every month is equivalent to fasting the whole month and performing its voluntary acts."