Deuteronomy 19:3-10

3You shall prepare the 1roads for yourself, and divide into three parts the territory of your land which the Lord your God will give you as a possession, 2so that any manslayer may flee there.

4“3Now this is the case of the manslayer who may flee there and live: when he 4kills his friend 5unintentionally, 6not hating him previously-- 5as when a man goes into the forest with his friend to cut wood, and his hand 7swings the axe to cut down the tree, and the iron head slips off the 8handle and 9strikes his friend so that he dies--he may flee to one of these cities and live; 6otherwise the avenger of blood might pursue the manslayer 10in the heat of his anger, and overtake him, because the way is long, and 11take his life, though he was not deserving of death, since he had not hated him previously. 7Therefore, I command you, saying, ‘You shall set aside three cities for yourself.’

8“If the Lord your God 12enlarges your territory, just as He has sworn to your fathers, and gives you all the land which He 13promised to give your fathers-- 9if you 14carefully observe all this commandment which I command you today, 15to love the Lord your God, and to walk in His ways always--16then you shall add three more cities for yourself, besides these three. 10So innocent blood will not be shed in the midst of your land which the Lord your God gives you as an inheritance, and 17bloodguiltiness be on you.