Amr bin Shurahbil reported,

A man came to the Messenger of Allah ﷺ and said, "Messenger of Allah, what do you say about a man who fasts the entire year?"The Messenger of Allah ﷺ replied, "I would have wished that he had not eaten anything throughout the year."The man asked, "What about two-thirds of it?"He said, "Even more."The man asked, "Then half of it?"He said, "Even more."Then he said, "Shall I not tell you of what removes the rancor of the heart?"They said, "Yes, indeed."He said, "Fasting three days of every month."

Nasai 2388

Sahih

أخبرنا محمد بن العلاء قال حدثنا أبو معاوية قال حدثنا الأعمش عن أبي عمار

عن عمرو بن شرحبيل قال

أتى رسول الله ﷺ رجل فقال يا رسول الله ما تقول في رجل صام الدهر كله فقال رسول الله ﷺ وددت أنه لم يطعم الدهر شيئا قال فثلثيه قال أكثر قال فنصفه قال أكثر قال أفلا أخبركم بما يذهب وحر الصدر قالوا بلى قال صيام ثلاثة أيام من كل شهر

النسائي 2388صحيح
Contents
Reference
Commentary
Ayat
Collection
Sunan Nasai Sughra
Book
Fasting
Chapter
Fasting two-thirds of the time, and mention of the disagreement among narrators of the report regarding that
Numbering
Darussalam 2388
Nasai 2388