Deuteronomy 19:1

Laws Concerning Manslaughter

19:1 When the Lord your God destroys the nations whose land he is about to give you and you dispossess them and settle in their cities and houses,

Deuteronomy 19:9

19:9 and then you are careful to observe all these commandments I am giving you today (namely, to love the Lord your God and to always walk in his ways), then you must add three more cities to these three.