Ghaylan bin Jarir غيلان بن جرير المعولي · The Book on Fasting

the Prophet said: "Fast the Day of Arafah, for indeed I anticipate that Allah will forgive (the sins) of the year after it, and the year before it."

the Prophet said: "Fast the Day of Ashura, for indeed I anticipate that Allah will forgive (the sins of) the year before it."

"It was said: 'O Messenger of Allah! What is the case of the one who fasts daily?' He said: 'He did not fast nor break (the fast).'" Or, he said: "He never fasted nor broke (his fast)."