Matthew 6:16-18 - The Sermon On The Mount: How To Fast
16 And when you fast, do not put on a sad countenance, as the hypocrites do; for they disfigure their faces, that they may appear to men to be fasting. Verily, I say to you, They have their reward. 17 But do you, when you fast, anoint your head and wash your face; 18 that you may not appear to men to be fasting, but to your Father who is in secret. And your Father who sees in secret will reward you.