'Fasting' in the Bible

“Whenever you fast, do not put on a gloomy face as the hypocrites do, for they neglect their appearance so that they will be noticed by men when they are fasting. Truly I say to you, they have their reward in full.

so that your fasting will not be noticed by men, but by your Father who is in secret; and your Father who sees what is done in secret will reward you.

[But this kind does not go out except by prayer and fasting.”]