Jesus' teaching on fasting

Mt 6:16 Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward.

Mt 6:17 But thou, when thou fastest, anoint thine head, and wash thy face;

Mt 6:18 That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly.