Deuteronomy 19:7-11

Wherefore I command thee, saying, Thou shalt separate three cities for thee.

And if the LORD thy God enlarge thy coast, as he hath sworn unto thy fathers, and give thee all the land which he promised to give unto thy fathers;

If thou shalt keep all these commandments to do them, which I command thee this day, to love the LORD thy God, and to walk ever in his ways; then shalt thou add three cities more for thee, beside these three:

That innocent blood be not shed in thy land, which the LORD thy God giveth thee for an inheritance, and so blood be upon thee.

But if any man hate his neighbour, and lie in wait for him, and rise up against him, and smite him mortally that he die, and fleeth into one of these cities: