'Fasting' in the Bible

"When any of you fast, never assume gloomy looks as the hypocrites do; for they disfigure their faces in order that it may be evident to men that they are fasting. I solemnly tell you that they already have their reward.

that it may not be apparent to men that you are fasting, but to your Father who is in secret; and your Father--He who sees in secret--will recompense you.

But an evil spirit of this kind is only driven out by prayer and fasting."