سنن النسائي

It was narrated that Muhajid said: "Abdullah bin 'Amr said to me: My father got me married to a woman from a noble family, and he used to come to her and ask her about her husband. She said: What a wonderful man he is! He never comes to my bed. And he has never approached me since he married me. He mentioned that to the Prophet (ﷺ) and he said: Bring him to me. So he brought him with him and (the Prophet) said: How do you fast? I said: "Every day." He said: "Fast three days of every month." I said: "I am able to do better than that." He said: "Fast for two days, and break your fast for one day." He said; "I am able to do better than that". He said: "Observe the best of fasts, the fast of Dawud, peace be upon him: Fasting for one day and breaking the fast for one day." 'Ata said: "someone who heard him told me that Ibn 'Umar (said) that the Prophet (ﷺ) said: 'Whoever fasts every day of his life, then he has not fasted."