Deuteronomy 19:5-7

Living Bible

⁵ If a man goes into the forest with his neighbor to chop wood, and the axhead flies off the handle and kills the man’s neighbor, he may flee to one of those cities and be safe. ^6-7 Anyone seeking to avenge the death will not be able to. These cities must be scattered so that one of them will be reasonably close to everyone; otherwise the angry avenger might catch and kill the innocent slayer, even though he should not have died since he had not killed deliberately.