Numbers 35:26-28

26But if the manslayer at any time goes outside the limits of the city of refuge where he fled,

27and the avenger of blood finds him outside the limits of his city of refuge, and the avenger of blood kills 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 may return to the land of his possession.