Numbers 35:25-28

The congregation shall deliver the manslayer from the hand of the blood avenger, and the congregation shall restore him to his city of refuge to which he 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 at any time goes beyond the border of his city of refuge to which he may flee, and the blood avenger finds him outside the border of his city of refuge, and the blood avenger kills the manslayer, he will not be guilty of blood because he should have remained in his city of refuge until the death of the high priest. But after the death of the high priest the manslayer shall return to the land of his possession.