It was narrated from ‘Abdullah bin ‘Amr that the Messenger of Allah ﷺ said to him: “Fast one day, and you will have the reward of what is left.” He said: “I am able to do more than that.” He said: “Fast two days and you will have the reward of what is left.” He said: “I am able to do more than that.” He said: “Fast three days and you will have the reward of what is left.” He said: “I am able to do more than that.” He said: “Fast four days and you will have the reward of what is left.” He said: “I am able to do more than that.” He said: “Observe the best kind of fasting before Allah, the fast of Dawud علیہ السلام; he used to fast one day and break his fast for one day.” (Sahih)