Numbers 35:25-28

25And the congregation shall deliver the slayer out of the hand of the avenger of blood, and the congregation shall restore him to the city of his refuge, where he had fled: and he shall abide in it to the death of the high priest, who was anointed with the holy oil. 26But if the slayer shall at any time come outside the border of the city of his refuge, where he had fled; 27And the avenger of blood find him outside the borders of the city of his refuge, and the avenger of blood shall kill the slayer; he shall not be guilty of blood:1 28Because he should have remained in the city of his refuge until the death of the high priest: but after the death of the high priest the slayer shall return into the land of his possession.