Positive commandment · Mitzvat Aseh #183 of 613
To give the Levites cities in which to dwell - they also serve as refuge centers
לתת ללויים ערים לשבת, וגם הן קולטות
The verse · Bamidbar 35:2
צַו אֶת־בְּנֵי יִשְׂרָאֵל וְנָתְנוּ לַלְוִיִּם מִנַּחֲלַת אֲחֻזָּתָם עָרִים לָשָׁבֶת וּמִגְרָשׁ לֶעָרִים סְבִיבֹתֵיהֶם תִּתְּנוּ לַלְוִיִּם
“Command the children of Yisra᾽el, that they give to the Levites of the inheritance of their possession cities to dwell in; and you shall give also to the Levites an open space for the cities round about them.”
The Rambam’s words
To give the Levites cities in which to dwell - they also serve as refuge centers - as [Numbers 35:2] states: "And you shall give cities to the Levites...."
לתת ללויים ערים לשבת, וגם הן קולטות, שנאמר: "ונתנו ללויים . . . ערים" (במדבר לה,ב).
Why · Sefer HaChinuch #408
The commandment on Israel to give cities within which the Levites may dwell, and they shelter
“The root of this commandment is well-known, as the tribe of Levi was from the select of the tribes and prepared for the service of the House of G-d, and [so] they did not have a portion with Israel in the inheritance of fields and vineyards.”
Who & when
“And this commandment is practiced at the time that Israel is dwelling on its land.”
Where in the Mishneh Torah
Hilchot Sabbatical Year and the Jubilee הלכות שמיטה ויובל