Matthew 6:16-18

When you fast, do not be somber like the hypocrites, for they disfigure their faces to show men they are fasting. Truly I tell you, they already have their full reward. But when you fast, anoint your head and wash your face, so that your fasting will not be obvious to men, but only to your Father, who is unseen. And your Father, who sees what is done in secret, will reward you.