Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with them both) narrates that the Messenger of Allah (peace and blessings be upon him) said to me: "Have I not been informed that you are one who fasts by day and one who stands in prayer by night?" He said: I said: Yes, O Messenger of Allah (peace and blessings be upon him)! It is so. So he (peace and blessings be upon him) said: "Do not do so; rather, sleep and stand in prayer, fast and break your fast. Your body has a right over you, your eyes have a right over you, your wife has a right over you, and your guest has a right over you. It is sufficient for you to fast three days every month, for every good deed is (rewarded) tenfold; when you do this, you will be one who fasts perpetually." He said: I was strict, so strictness was imposed on me as well. I said: O Messenger of Allah (peace and blessings be upon him)! I have the strength. He (peace and blessings be upon him) said: "Then fast three days every week." He said: I was strict, so strictness was imposed on me. I said: O Messenger of Allah (peace and blessings be upon him)! I am able. He (peace and blessings be upon him) said: "Then keep the fasts of the Prophet of Allah, Dawud (peace be upon him), and do not exceed that." He said: I said: What were the fasts of the Prophet of Allah, Dawud (peace be upon him)? He (peace and blessings be upon him) said: "Half of the year."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8474