Negative commandment · Lo Ta’aseh #309 of 613
To not work or sow in that land
שלא לעבוד ולזרוע בנחל איתן
The verse · Devarim 21:4
וְהוֹרִדוּ זִקְנֵי הָעִיר הַהִוא אֶת־הָעֶגְלָה אֶל־נַחַל אֵיתָן אֲשֶׁר לֹא־יֵעָבֵד בּוֹ וְלֹא יִזָּרֵעַ וְעָרְפוּ־שָׁם אֶת־הָעֶגְלָה בַּנָּחַל
“and the elders of that city shall bring down the heifer to a rough ravine, which is neither ploughed nor sown, and shall break the heifer’s neck there in the ravine:”
The Rambam’s words
Not to till or sow the land [around] a powerful river [at which atonement was made for an unsolved murder], as [Deuteronomy 21:4] states: "...which must never be tilled and never be sown."
שלא לעבוד ולזרוע בנחל איתן, שנאמר "אשר לא ייעבד בו, ולא ייזרע" (דברים כא,ד).
Why · Sefer HaChinuch #531
To not work or sow in that land
“It is from the roots of the commandment [that it is] in order that the heart of the people be aroused in their seeing this great procedure — the gathering of the elders of the city and its great men: And they take a cow, which is a large animal, and they go outside of the city in assembly, and with the masses — since everyone wants to see these things.”
Who & when
“And this prohibition is practiced by males and females.”
Where in the Mishneh Torah
Hilchot Murderer and the Preservation of Life הלכות רוצח ושמירת נפש