Matthew 6:16-18

16Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear to men to fast. Verily I say to you, They have their reward. 17But thou, when thou fastest, anoint thy head, and wash thy face; 18That thou mayest not appear to men to fast, but to thy Father who is in secret: and thy Father, who seeth in secret, shall reward thee openly.