Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 228

שלא לשנות מגרשי הלויים ושדותיהם, שנאמר "ושדה מגרש עריהם, לא יימכר" (ויקרא כה,לד); מפי השמועה למדו שזו אזהרה שלא ישתנה.

Not to change [the purpose of] the open areas and fields [granted to] the Levites, as [Leviticus 25:34] states: "The fields of the open areas [surrounding] their cities shall not be sold." According to the oral tradition, we have learned that this verse is a prohibition against changing [the purpose for which these lands are used].