Dora Bas Rivka Silver O'H
After he was expelled from the fish, G-d spoke to Jonah again. He told Jonah to go to Nineveh and this time to do what G-d says. Nineveh was a particularly large city for the time, a three-day walk around the perimeter. Jonah walked through the city and proclaimed that in forty days, the city would be overturned. (Rashi explains that it would be "overturned" rather than "destroyed" because overturned could also have a positive connotation, i.e. spiritually overturned through repentance.) The people heeded Jonah, donning sackcloth and fasting.
When the king of Nineveh heard about this, he got off his throne and joined his people sitting in ashes. He had it announced throughout his kingdom that everyone should fast and wear sackcloth, both man and beast. The people were to cry out to G-d and renounce their evil ways. G-d saw their sincerity and agreed not to demolish the city.