Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 182
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 182, with English translation by Maimonides (Rambam).
להכין שש ערי מקלט, שנאמר: "תכין לך, הדרך, ושילשת" (דברים יט,ג).
To prepare six refuge cities, as [Deuteronomy 19:3] states: "Prepare the way and divide into three [the boundary]...."