Mattityahu (Mat) 6:16-18

“Now when you fast, don’t go around looking miserable, like the hypocrites. They make sour faces so that people will know they are fasting. Yes! I tell you, they have their reward already! But you, when you fast, wash your face and groom yourself, so that no one will know you are fasting — except your Father, who is with you in secret. Your Father, who sees what is done in secret, will reward you.