Deuteronomy 19:8

⁶  Lest the avenger of the blood pursue the slayer, while his heart is hot, and overtake him, because the way is long, and slay him; whereas he was not worthy of death, inasmuch as he hated him not in time past.

⁷  Wherefore I command thee, saying, Thou shalt separate three cities for thee.

⁸  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;

⁹  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:

¹⁰  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.