question #3 Sahih Muslim 1159o, Book 13, Hadith 249 : What can be learned from the fasting practice of Prophet David (peace be upon him) as mentioned in Islamic teachings?

Then observe the fast of David (peace be upon him). Observe fast one day and break it (on the other) day. And he (‘Abdullah b. ‘Amr) used to say: Would that I had availed myself of this concession.