Musnad Abu Ya'la al-Mawsili 2:5

Shayban narrated to us, Abu Hilal narrated to us, Ghaylan ibn Jarir narrated to us, Abdullah ibn Ma'bad al-Zamani narrated to me, from Umar ibn al-Khattab, who said: We were with the Messenger of Allah (may Allah bless him and grant him peace) when he came upon a man, and it was said, "He has not broken his fast since such and such [a time]." He said, "He has neither fasted nor broken his fast," or "He did not fast and he did not break his fast" (Ghaylan was in doubt). When Umar saw the anger of the Prophet (may Allah bless him and grant him peace), he said, "O Messenger of Allah, [what about] fasting two days and breaking the fast for one?" He said, "And who can endure that?" He said, "I said, 'O Messenger of Allah, [what about] fasting one day and breaking the fast for one?'" He said, "That is the fasting of my brother David." He said, "O Messenger of Allah, [what about] fasting one day and breaking the fast for two?" He said, "And who can endure that?" He said, "O Messenger of Allah, [what about] fasting on Monday?" He said, "That is a day I was born on, and the day the Prophethood was sent down upon me." He said, "O Messenger of Allah, [what about] fasting the day of Arafah and the day of Ashura?" He said, "One of them expiates [sins]," and he said regarding the other, "what is before it or what is after it" (Abu Hilal was in doubt).