Numbers 35:25-28

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.