Negative commandment · Lo Ta’aseh #228 of 613
To not change the open areas of the Levites
שלא לשנות מגרשי הלויים ושדותיהם
The verse · Vayikra 25:34
וּשְׂדֵה מִגְרַשׁ עָרֵיהֶם לֹא יִמָּכֵר כִּי־אֲחֻזַּת עוֹלָם הוּא לָהֶם
“But the field of the pasture lands of their cities may not be sold; for it is their perpetual possession.”
The Rambam’s words
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].
שלא לשנות מגרשי הלויים ושדותיהם, שנאמר "ושדה מגרש עריהם, לא יימכר" (ויקרא כה,לד); מפי השמועה למדו שזו אזהרה שלא ישתנה.
Why · Sefer HaChinuch #342
To not change the open areas of the Levites
“It is from the roots of the commandment [that it is] because the cities of the Levites were prepared for the needs of all the other tribes; as it was the tribe that was selected for the service of G-d — and all of their efforts were about wisdom, as they were not preoccupied with the working of the land like the rest of the tribes of Israel.”
Who & when
“And this commandment is practiced in the Land of Israel at the time when Israel is there — whether by Levites or by Israelites — by males and females, as all are obligated never to change the three places spoken about: the city; the open space; and the fields and vineyards.”
Where in the Mishneh Torah
Hilchot Sabbatical Year and the Jubilee הלכות שמיטה ויובל