Numbers 35:26-28

26“If the one who kills someone ever goes outside the border of the city of refuge he fled to,

27and the avenger of blood finds him outside the border of his city of refuge and kills him, the avenger will not be guilty of bloodshed,

28for the one who killed a person was supposed to live in his city of refuge until the death of the high priest. Only after the death of the high priest may the one who has killed a person return to the land he possesses.