God told Moses to designate six cities in the promised land as cities of refuge where someone who killed another accidentally could flee to avoid punishment.
And the LORD spoke to Moses, saying, “Speak to the people of Israel and say to them, When you cross the Jordan into the land of Canaan, then you shall select cities to be cities of refuge for you, that the manslayer who kills any person without intent may flee there. The cities shall be for you a refuge from the avenger, that the manslayer may not die until he stands before the congregation for judgment. And the cities that you give shall be your six cities of refuge.”
When someone asked for refuge there would be an inquiry to find out if he was entitled to it.
But if he pushed him suddenly without enmity, or hurled anything on him without lying in wait or used a stone that could cause death, and without seeing him dropped it on him, so that he died, though he was not his enemy and did not seek his harm, then the congregation shall judge between the manslayer and the avenger of blood, in accordance with these rules. And the congregation shall rescue the manslayer from the hand of the avenger of blood, and the congregation shall restore him to his city of refuge to which he had fled, and he shall live in it until the death of the high priest who was anointed with the holy oil.
But if the manslayer shall at any time go beyond the boundaries of his city of refuge to which he fled, and the avenger of blood finds him outside the boundaries of his city of refuge, and the avenger of blood kills the manslayer, he shall not be guilty of blood.