Deuteronomy 19:6-8

Darby Translation

⁶ lest the avenger of blood pursue the manslayer, while his heart is hot, and overtake him, because the way is long, and smite him mortally; whereas he was not worthy of death, since he hated him not previously.

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

⁸ And 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