Deuteronomy 19:8-10

8And if the LORD thy God enlarge thy border, as he hath sworn unto thy fathers, and give thee all the land which he promised to give unto thy fathers;

9if thou shalt keep all this commandment to do it, 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:

10that innocent blood be not shed in the midst of thy land, which the LORD thy God giveth thee for an inheritance, and so blood be upon thee.