'Fast' in the Bible

But when you fast, put oil on your head [as you normally would to groom your hair] and wash your face

Then the disciples of John [the Baptist] came to Jesus, asking, “Why do we and the Pharisees often fast [as a religious exercise], but Your disciples do not fast?”

And Jesus replied to them, “Can the guests of the bridegroom mourn while the bridegroom is with them? The days will come when the bridegroom is taken away from them, and then they will fast.