"I heard Mu'adhah saying to Aishah: 'Did the Messenger of Allah fast three days of every month?' She replied in the affirmative. So she said: 'Which of them would he fast?' She said: 'Which of them he would fast was not noticeable.'"
Jami` at-Tirmidhi Book 8, Hadith 82
← Previous Hadith "The Messenger of Allah said: 'Whoever fasts three days in every month, then that is (similar to) fasting every day.' Then Allah Mighty and Sublime is He, attested to that in His Book, by revealing: Whoever brings a good deed, shall have ten times the like thereof. So a day is like ten."

Jami` at-Tirmidhi Book 8, Hadith 81 Next Hadith → The Messenger of Allah said: "Indeed your Lord said: 'Every good deed is rewarded with ten of the same up to seven hundred times over. Fasting is for Me, and I shall reward for it.' Fasting is a shield from the Fire. The smell coming from the mouth of the one fasting is more pleasant to Allah than the scent of musk. If one of you is abused by an ignorant person while fasting, then let him say: 'Indeed I am fasting.'"

Jami` at-Tirmidhi Book 8, Hadith 83