'Fasting' in the Bible

“And whenever you are fasting, do not look gloomy like the hypocrites, for they put on a sad and dismal face [like actors, discoloring their faces with ashes or dirt] so that their fasting may be seen by men. I assure you and most solemnly say to you, they [already] have their reward in full.

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

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