Matthew 6:16-18

16“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.

17But when you fast, put oil on your head [as you normally would to groom your hair] and wash your face

18so 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.