It is narrated from Sayyiduna Ibn Amr (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said to me: "I have come to know that you fast all day and stand in prayer all night. Do not do so, for your body has a right over you, your eyes have a right over you, and your wife has a right over you. Fast only three days in every month; this will be equal to fasting all the time." I imposed hardship upon myself, so hardship was imposed upon me. I said, "I have strength for more than this." The Noble Prophet (peace and blessings be upon him) said: "Then fast three days in every week." I imposed hardship upon myself, so hardship was imposed upon me. I said, "O Messenger of Allah! I have strength for more than this." The Noble Prophet (peace and blessings be upon him) said: "Then adopt the way of Sayyiduna Dawud (peace be upon him): fast one day and leave fasting one day."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6867
Hadith Gradingحکم دارالسلام:حديث صحيح، خ: 1975، م: 1159، وهذا إسناد حسن