Deuteronomy 19:8

4 Now this is the situation regarding the manslayer who flees to one of these cities to save his life, having killed his neighbor accidentally, without intending to harm him:

5 If he goes into the forest with his neighbor to cut timber and swings his axe to chop down a tree, but the blade flies off the handle and strikes and kills his neighbor, he may flee to one of these cities to save his life.

6 Otherwise, the avenger of blood might pursue the manslayer in a rage, overtake him if the distance is great, and strike him dead though he did not deserve to die, since he did not intend any harm.

7 This is why I am commanding you to set apart for yourselves three cities.

8 And if the LORD your God enlarges your territory, as He swore to your fathers, and gives you all the land He promised them,

9 and if you carefully keep all these commandments I am giving you today, loving the LORD your God and walking in His ways at all times, then you are to add three more cities to these three.

10 Thus innocent blood will not be shed in the land that the LORD your God is giving you as an inheritance, so that you will not be guilty of bloodshed.

11 If, however, a man hates his neighbor and lies in wait, attacks him and kills him, and then flees to one of these cities,

12 the elders of his city must send for him, bring him back, and hand him over to the avenger of blood to die.

Read all of Deuteronomy 19