Numbers 35:22-28

22But if anyone pushes a person suddenly, without hostility, or throws an object at him unintentionally, 23or without looking drops a heavy stone that kills him, but he was not an enemy and did not intend to harm him, 24then the congregation must judge between the slayer and the avenger of blood according to these ordinances. 25The assembly is to protect the manslayer from the hand of the avenger of blood. Then the assembly will return him to the city of refuge to which he fled, and he must live there until the death of the high priest, who was anointed with the holy oil.

26But if the manslayer ever goes outside the limits of the city of refuge to which he fled 27and the avenger of blood finds him outside of his city of refuge and kills him, then the avenger will not be guilty of bloodshed, 28because the manslayer must remain in his city of refuge until the death of the high priest. Only after the death of the high priest may he return to the land he owns.