Matthew 6:16-18

And when you may fast, do not be as the hypocrites, of sour countenances, for they disfigure their faces, that they may appear to men fasting; truly I say to you that they have their reward. But you, fasting, anoint your head, and wash your face, that you may not appear to men fasting, but to your Father who [is] in secret, and your Father, who is seeing in secret, will reward you.