Matthew 6:6, 16

But thou, when thou prayest, enter into thine inner chamber, and having shut thy door, pray to thy Father who is in secret, and thy Father who seeth in secret shall recompense thee.

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