صحیح مسلم · Hadith 2737

Abdullah b. Amr (Allah be pleased with both of them) reported: The Messenger of Allah ( ‌صلی ‌اللہ ‌علیہ ‌وسلم ‌ ) said to me: 'Abdullah b. Amr, you fast continuously and stand in prayer for the whole of night. If you do like that, your eyes would be highly strained and would sink and lose sight. There is no (reward for) fasting (for him) who fasts perpetually. Fasting for three days during the month is like fasting, the whole of the month. I said: I am capable of doing more than this, whereupon he said: Observe the fast of David. He used to fast one day and break (the other) day. And he did not turn back in the encounter.