Numbers 35:22-25

22“But suppose someone pushes another person without having shown previous hostility, or throws something that unintentionally hits another person,

23or accidentally drops a huge stone on someone, though they were not enemies, and the person dies.

24If this should happen, the community must follow these regulations in making a judgment between the slayer and the avenger, the victim’s nearest relative:

25The 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.