Numbers 35:33 in the King James Version
So ye shall not pollute the land wherein ye are: for blood it defileth the land: and the land cannot be cleansed of the blood that is shed therein, but by the blood of him that shed it.
Context
32 “‘You shall take no ransom for him who has fled to his city of refuge, that he may come again to dwell in the land before the death of the priest.
33 “‘So you shall not pollute the land where you live; for blood pollutes the land. No atonement can be made for the land for the blood that is shed in it, but by the blood of him who shed it.
34 You shall not defile the land which you inhabit, where I dwell; for I, the LORD, dwell among the children of Israel.’”