Jonah 3:4-5

4Then on the first day’s walk, Jonah began to go through the city, and he called out and said, “Forty days more [remain] and [then] Nineveh will be overthrown!”

5The 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.