'Fast' in the Bible

Then the sailors were afraid, and each man cried out to his god; and to lighten the ship [and diminish the danger] they threw the ship’s cargo into the sea. But Jonah had gone below into the hold of the ship and had lain down and was sound asleep.

The people of Nineveh believed and trusted in God; and they proclaimed a fast and put on sackcloth [in penitent mourning], from the greatest even to the least of them.