Sahih Bukhari

Narrated `Abdullah bin `Amr bin Al-`As:Allah's Messenger (ﷺ) said to me, ""O `Abdullah! Have I not been informed that you fast during the day and offer prayers all the night."" `Abdullah replied, ""Yes, O Allah's Messenger (ﷺ)!"" The Prophet (ﷺ) said, ""Don't do that; fast for few days and then give it up for few days, offer prayers and also sleep at night, as your body has a right on you, and your wife has a right on you, and your guest has a right on you. And it is sufficient for you to fast three days in a month, as the reward of a good deed is multiplied ten times, so it will be like fasting throughout the year."" I insisted (on fasting) and so I was given a hard instruction. I said, ""O Allah's Messenger (ﷺ)! I have power."" The Prophet (ﷺ) said, ""Fast like the fasting of the Prophet David (ﷺ) and do not fast more than that."" I said, ""How was the fasting of the Prophet of Allah, David (ﷺ)?"" He said, ""Half of the year,"" (i.e. he used to fast on every alternate day). Afterwards when `Abdullah became old, he used to say, ""It would have been better for me if I had accepted the permission of the Prophet (which he gave me i.e. to fast only three days a month)