Deuteronomy 19:4-14

4 Now this is the case of a homicide who might flee there and live, that is, someone who has killed another person unintentionally when the two had not been at enmity before:
5 Suppose someone goes into the forest with another to cut wood, and when one of them swings the ax to cut down a tree, the head slips from the handle and strikes the other person who then dies; the killer may flee to one of these cities and live.
6 But if the distance is too great, the avenger of blood in hot anger might pursue and overtake and put the killer to death, although a death sentence was not deserved, since the two had not been at enmity before.
7 Therefore I command you: You shall set apart three cities.
8 If the Lord your God enlarges your territory, as he swore to your ancestors—and he will give you all the land that he promised your ancestors to give you,
9 provided you diligently observe this entire commandment that I command you today, by loving the Lord your God and walking always in his ways—then you shall add three more cities to these three,
10 so that the blood of an innocent person may not be shed in the land that the Lord your God is giving you as an inheritance, thereby bringing bloodguilt upon you.
11 But if someone at enmity with another lies in wait and attacks and takes the life of that person, and flees into one of these cities,
12 then the elders of the killer's city shall send to have the culprit taken from there and handed over to the avenger of blood to be put to death.
13 Show no pity; you shall purge the guilt of innocent blood from Israel, so that it may go well with you.
14 You must not move your neighbor's boundary marker, set up by former generations, on the property that will be allotted to you in the land that the Lord your God is giving you to possess.
New Revised Standard Version Bible, copyright 1989, Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved.