The Prophet (ﷺ) said (to `Abdullah), "Fast three days a month." `Abdullah said, (to the Prophet) "I am able to fast more than that." They kept on arguing on this matter till the Prophet (ﷺ) said, "Fast on alternate days, and recite the whole Quran once a month." `Abdullah said, "I can recite more (in a month)," and the argument went on till the Prophet (ﷺ) said, "Recite the Quran once each three days." (i.e. you must not recite the whole Quran in less than three days).
Sahih al-Bukhari Book 30, Hadith 85
← Previous Hadith The news of my daily fasting and praying every night throughout the night reached the Prophet. So he sent for me or I met him, and he said, "I have been informed that you fast everyday and pray every night (all the night). Fast (for some days) and give up fasting (for some days); pray and sleep, for your eyes have a right on you, and your body and your family (i.e. wife) have a right on you." I replied, "I have more power than that (fasting)." The Prophet (ﷺ) said, "Then fast like the fasts of (the Prophet) David". I said, "How?" He replied, "He used to fast on alternate days, and he used not to flee on meeting the enemy." I said, "From where can I get that chance?" (`Ata' said, "I do not know how the expression of fasting daily throughout the life occurred.") So, the Prophet (ﷺ) said, twice, "Whoever fasts daily throughout his life is just as the one who does not fast at all."

Sahih al-Bukhari Book 30, Hadith 84 Next Hadith → The Prophet (ﷺ) said to me, "You fast daily all the year and pray every night all the night?" I replied in the affirmative. The Prophet (ﷺ) said, "If you keep on doing this, your eyes will become weak and your body will get tired. He who fasts all the year is as he who did not fast at all. The fasting of three days (a month) will be equal to the fasting of the whole year." I replied, "I have the power for more than this." The Prophet (ﷺ) said, "Then fast like the fasting of David who used to fast on alternate days and would never flee from the battle field, on meeting the enemy."

Sahih al-Bukhari Book 30, Hadith 86