Deuteronomy 19:2-4

Amplified Bible

² you shall designate three cities for yourself in the central area of the land, which the Lord your God is giving you to possess. ³ You shall prepare and maintain for yourself the roads [to these cities], and divide the territory of your land into three parts, so that anyone who kills another unintentionally may escape there [for asylum].

⁴ “Now this is the case of the offender (manslayer) who may escape there and live [protected from vengeance]: when he kills his neighbor unintentionally, not having hated him previously—