'Fast' in the Bible

And when ye fast, be not as the hypocrites, downcast in countenance; for they disfigure their faces, so that they may appear fasting to men: verily I say unto you, They have their reward.

Then come to him the disciples of John, saying, Why do we and the Pharisees often fast, but thy disciples fast not?

And Jesus said to them, Can the sons of the bridechamber mourn so long as the bridegroom is with them? But days will come when the bridegroom will have been taken away from them, and then they will fast.