In the narration of Sayyiduna Abdullah bin Amr رضي الله عنه, it is stated: Observe fasting like the fasts of Dawud عليه السلام, for they are the best and most moderate fasts in the sight of Allah Almighty.

The best of fasts are the fasts of Prophet Dawud (peace be upon him). I have mentioned the chains of these narrations in Kitab al-Kabir.

Sayyiduna Abdullah bin Amr (may Allah be pleased with him) narrates that news reached the Noble Prophet (peace and blessings be upon him) that I fast continuously and pray all night. He says that either you sent someone to call me, or I met you, so you said: "Has it not been conveyed to me that you fast continuously and pray all night? Do not do so. For your eyes have a right over you, your soul has a right over you, and your family has a share (portion) over you. Fast and also leave fasting, pray at night and also sleep, and fast one day in every ten days, and you will get the reward of the remaining nine days as well." He says: "Indeed, I have the strength for more than this, O Messenger of Allah." You said: "Then observe the fasts of Dawud (peace be upon him)." He asked: "O Messenger of Allah, how did Dawud (peace be upon him) fast?" The Prophet (peace and blessings be upon him) said: "He would fast one day and leave fasting one day. And when he faced the enemy, he would not flee." He said: "O Prophet of Allah, how can I attain this honor?" Janab Ata says: "I do not know how the mention of perpetual fasting came up." So the Noble Prophet (peace and blessings be upon him) said: "Whoever fasts perpetually has not fasted at all." This hadith is from Barsani. In the narration of Janab Abdur Razzaq, it is mentioned: He said, "Indeed, I fast consecutively," and he said, "Either you sent someone to call me." And he said, "Indeed, I find strength for more than this."

Sayyiduna Abdullah bin Amr bin Al-As (may Allah be pleased with him) narrates that the Messenger of Allah (peace be upon him) sent a message to call me. (When I presented myself) the Prophet (peace be upon him) said: "Has it not been reported to me that you spend the whole night in voluntary prayers and fast during the day?" Then the complete hadith was narrated. He says that the Noble Prophet (peace be upon him) said: "Observe the fast of Dawud (peace be upon him), for he was the most devoted worshipper among people. He would fast one day and leave fasting the next day." Then he said: "Indeed, you do not know; perhaps you may be granted a long life." He says that now I wish I had accepted the concession which the Messenger of Allah (peace be upon him) had given me.

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."

Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) reports that the Messenger of Allah (peace and blessings be upon him) said: "Whoever fasts for one day in the way of Allah, Allah, because of that day, will keep his face seventy years' distance away from the fire of Hell."

It is narrated from Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) that the Prophet Muhammad (peace and blessings be upon him) said: "Whoever fasts for one day in the way of Allah, seeking Allah's pleasure, Allah will place a distance of seventy years between his face and the fire of Hell."

Sayyiduna Abu Ayyub Ansari (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Whoever fasts in the month of Ramadan and then follows it with six days of fasting in the month of Shawwal, it is as if he has fasted for the entire year."