Deuteronomy 19:4-5

4“Here is the law concerning a case of someone who kills a person and flees there to save his life, having killed his neighbor accidentally without previously hating him:

5If, for example, he goes into the forest with his neighbor to cut timber, and his hand swings the ax to chop down a tree, but the blade flies off the handle and strikes his neighbor so that he dies, that person may flee to one of these cities and live.