'Fast' in the Bible

"Whenever you fast, do not be sullen like the hypocrites, for they make their faces unrecognizable in order that they may be seen fasting by people. Truly I say to you, they have received their reward in full!

Then the disciples of John approached him, saying, "Why do we and the Pharisees fast often, but your disciples do not fast?"

And Jesus said to them, "{The bridegroom's attendants} are not able to mourn as long as the bridegroom is with them. But days are coming when the bridegroom is taken away from them, and then they will fast.