Numbers 35:25-28

The congregation shall rescue the offender from the hand of the blood avenger and return him to his city of refuge, [the place] to which he had escaped; and he shall live there until the death of the high priest who was anointed with the sacred oil. But if at any time the one guilty of manslaughter comes outside the border of his city of refuge to which he fled, and the blood avenger finds him outside the border of his city of refuge and kills the offender, the blood avenger will not be guilty of murder, because the offender should have remained in his city of refuge until the death of the high priest. But after the high priest’s death the offender shall return to the land of his possession.