Deuteronomy 19:2-4

New Century Version

² Then choose three cities in the middle of the land the Lord your God is giving you as your own. ³ Build roads to these cities, and divide the land the Lord is giving you into three parts so that someone who kills another person may run to these cities.

⁴ This is the rule for someone who kills another person and runs to one of these cities in order to save his life. But the person must have killed a neighbor without meaning to, not out of hatred.