Matthew 6:16-18 - The Sermon On The Mount: How To Fast
16 And when you may fast, be not like the hypocrites, of a sad contenance: for they disfigure their faces, in order that they may appear unto the people fasting. Truly I say unto you, They exhaust their reward. 17 But thou, fasting, anoint thy head, and wash thy face; 18 in order that thou mayest not appear unto the people fasting, but to thy Father who is in secret: and thy Father, who seeth in secret, will reward thee openly.