Abu Qatada reported,
Umar bin Khattab asked, "Messenger of Allah, what about one who fasts two days and breaks his fast for one?"He replied, "Can anyone manage that?"Umar asked, "Messenger of Allah, what about one who fasts a day and breaks his fast a day?"He replied, "That is the fast of Dawud."Umar asked, "What about one who fasts a day and breaks his fast for two?"He replied, "I wish I were given the strength for that."
Azami 4470
Sahihعن أبي قتادة، قال
قال عمر بن الخطاب: يا رسول الله، كيف بمن يصوم يومين ويفطر يوما؟ قال: ويطيق ذلك أحد؟ قال: يا رسول الله، كيف بمن يصوم يوما ويفطر يوما؟ قال: ذلك صوم داود. قال: كيف بمن يصوم يوما ويفطر يومين؟ قال: وددت أني طوقت ذلك.
Muslim narrated it in the Book of Fasting (1162) through several routes from Hammad bin Zayd, from Ghaylan, from Abdullah bin Mabad Zimmani, from Abu Qatada, who mentioned it in a long hadith concerning the prohibition of fasting continuously throughout the year.