Deuteronomy 19:2-9

21you shall set aside for yourself three cities in the midst of your land which the Lord your God is giving you to 2possess. 3You shall prepare the 3roads for yourself, and divide into three regions the territory of your land which the Lord your God will give you as an inheritance, 4so that anyone who commits manslaughter may flee there.

4“5Now this is the case of the one who commits manslaughter, who may flee there and live: when he 6kills his friend 7unintentionally, 8not hating him previously-- 5as when a person goes into the forest with his friend to cut wood, and his hand 9swings the axe to cut down the tree, and the iron head slips off the 10handle and 11strikes his friend so that he dies--he may flee to one of these cities and live. 6Otherwise, the avenger of blood might pursue 12him 13in the heat of his anger, and overtake him because the way is long, and 14take his life, though he was not sentenced to death since he had not hated him previously. 7Therefore I command you, saying, ‘You shall set aside for yourself three cities.’

8“And if the Lord your God 15enlarges your territory, just as He has sworn to your fathers, and gives you all the land that He 16promised to give your fathers-- 9if you 17carefully follow all of this commandment which I am commanding you today, 18to love the Lord your God, and to walk in His ways always--19then you shall add three more cities for yourself, besides these three.