Deuteronomy 19:8; Deuteronomy 19:9

8 And if the LORD your God enlarges your territory, as he has sworn to your fathers, and gives you all the land that he promised to give to your fathers--

9 provided you are careful to keep all this commandment, which I command you today, by loving the LORD your God and by walking ever in his ways--then you shall add three other cities to these three,