Sahih Bukhari

Narrated `Abdullah bin `Amr:Allah's Messenger (ﷺ) entered upon me and said, ""Have I not been informed that you offer prayer all the night and fast the whole day?"" I said, ""Yes."" He said, ""Do not do so; Offer prayer at night and also sleep; Fast for a few days and give up fasting for a few days because your body has a right on you, and your eye has a right on you, and your guest has a right on you, and your wife has a right on you. I hope that you will have a long life, and it is sufficient for you to fast for three days a month as the reward of a good deed, is multiplied ten times, that means, as if you fasted the whole year."" I insisted (on fasting more) so I was given a hard instruction. I said, ""I can do more than that (fasting)"" The Prophet said, ""Fast three days every week."" But as I insisted (on fasting more) so I was burdened. I said, ""I can fast more than that."" The Prophet (ﷺ) said, ""Fast as Allah's prophet David used to fast."" I said, ""How was the fasting of the prophet David?"" The Prophet (ﷺ) said, ""One half of a year (i.e. he used to fast on alternate days)