Hadith 2111
Sayyiduna Abu Qatadah (may Allah be pleased with him) narrates that Sayyiduna Umar (may Allah be pleased with him) asked the Messenger of Allah (peace and blessings be upon him), "What is the state of the person who fasts for two days and leaves one day?" The Prophet (peace and blessings be upon him) said: "Can anyone bear that?" So he asked, "What about the person who fasts one day and leaves one day?" The Prophet (peace and blessings be upon him) said: "This is the way of the fasts of Dawud (peace be upon him)." He asked, "Then what about the person who fasts one day and does not fast for two days?" The Prophet (peace and blessings be upon him) said: "It is my wish and desire that I also had the strength for that."