Deuteronomy 19:8-10

8And if Jehovah 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 Jehovah thy God, and to walk ever in his ways; then shalt thou add three cities more for thee, besides these three: 10that innocent blood be not shed in the midst of thy land, which Jehovah thy God giveth thee for an inheritance, and so blood be upon thee.