Numbers 35:31-33

Lexham English Bible

³¹ Also, you will not take a ransom payment for the life of a killer who is guilty of death; indeed, he must surely be put to death. ³² You will not take a ransom payment for the one that flees to the city of his refuge, so that he may return to live in the land before the death of the priest. ³³ So you will not pollute the land in which you are; because blood pollutes the land, and no atonement can be made for the land for the blood that is poured out on it except with the blood of the one who poured it out.