Numbers 35:25-28

The community must protect the slayer from the avenger and must escort the slayer back to live in the city of refuge to which he fled. There he must remain until the death of the high priest, who was anointed with the sacred oil. “But if the slayer ever leaves the limits of the city of refuge, and the avenger finds him outside the city and kills him, it will not be considered murder. The slayer should have stayed inside the city of refuge until the death of the high priest. But after the death of the high priest, the slayer may return to his own property.