Numbers 35:26-28

26But if the manslayer shall at any time go beyond the border of his city of refuge, whither he fleeth;

27and the avenger of blood find him without the border of his city of refuge, and the avenger of blood slay the manslayer; he shall not be guilty of blood:

28because 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 into the land of his possession.