Deuteronomy 19:2-13

MLV(i) 2 you will set apart three cities for you in the midst of your land, which Jehovah your God gives you to possess it. 3 You will prepare for you the way and divide the borders of your land, which Jehovah your God causes you to inherit, into three parts, that every manslayer may flee there.
4 And this is the case of the manslayer, who will flee there and live: Whoever kills his neighbor unawares and did not hate him in time past, 5 as when a man goes into the forest with his neighbor to hew wood and his hand fetches a stroke with the axe to cut down the tree and the head slips from the helve and lands upon his neighbor, so that he dies, he will flee to one of these cities and live.
6 Lest the avenger of blood pursue the manslayer, while his heart is hot and overtake him, because the way is long and kill* him mortally, and he was not worthy of death, inasmuch as he did not hate him in time past.
7 Therefore I command you, saying, You will set apart three cities for you. 8 And if Jehovah your God enlarge your border, as he has sworn to your fathers and give you all the land which he promised to give to your fathers, 9 if you will keep all this commandment to do it, which I command you this day, to love Jehovah your God and to walk ever in his ways, then will you add three more cities for you, besides these three, 10 that innocent blood not be shed in the midst of your land, which Jehovah your God gives you for an inheritance and so blood be upon you.
11 But if any man hates his neighbor and lies in wait for him and rises up against him and slays him mortally so that he dies and he flees into one of these cities, 12 then the elders of his city will send and fetch him from there and deliver him into the hand of the avenger of blood, that he may die.
13 Your eye will not pity him, but you will put away the innocent blood from Israel, that it may go well with you.