Deuteronomy 19:9-11

9provided you keep every one of these commands I am giving you today and follow them, loving the Lord your God and walking in his ways at all times — you are to add three more cities to these three.

10In this way, innocent blood will not be shed, and you will not become guilty of bloodshed in the land the Lord your God is giving you as an inheritance.

11But if someone hates his neighbor, lies in ambush for him, attacks him, and strikes him fatally, and flees to one of these cities,