Numbers 35:16

“But if he did not lie in wait for him, but God let him fall into his hand, then I will appoint you a place to which he may flee.

‘If anyone strikes down a person, the murderer shall be put to death at the mouth of witnesses, but no person shall be put to death on the testimony of one witness.

“Now this is the case of the manslayer who may flee there and live: when he strikes down his friend without premeditation, not hating him previously—

“But if there is a man who hates his neighbor and lies in wait for him and rises up against him and strikes down his life so that he dies, and he flees to one of these cities,

“Speak to the sons of Israel, saying, ‘Designate the cities of refuge, of which I spoke to you by the hand of Moses,

These were the appointed cities for all the sons of Israel and for the sojourner who sojourns among them, that whoever strikes down any person unintentionally may flee there and not die by the hand of the avenger of blood until he stands before the congregation.