Deuteronomy 19:6-8

Young's Literal Translation

⁶ lest the redeemer of blood pursue after the man-slayer when his heart is hot, and hath overtaken him (because the way is great), and hath smitten him -- the life, and he hath no sentence of death, for he is not hating him heretofore;

⁷ therefore I am commanding thee, saying, Three cities thou dost separate to thee.

⁸ `And if Jehovah thy God doth enlarge thy border, as He hath sworn to thy fathers, and hath given to thee all the land which He hath spoken to give to thy fathers --