Negative commandment · Lo Ta’aseh #296 of 613
Not to take a ransom in return for exile for a person who kills accidentally
שלא ליקח כופר בגלות רוצח בשגגה
The verse · Bamidbar 35:32
וְלֹא־תִקְחוּ כֹפֶר לָנוּס אֶל־עִיר מִקְלָטוֹ לָשׁוּב לָשֶׁבֶת בָּאָרֶץ עַד־מוֹת הַכֹּהֵן
“And you shall take no ransom for him that is fled to the city of his refuge, that he should come back to dwell in the land, until the death of the priest.”
The Rambam’s words
Not to take a ransom in return for exile for a person who kills accidentally, as [Numbers 35:32] states: "And do not take a ransom [for having] to flee to his refuge city."
שלא ליקח כופר בגלות רוצח בשגגה, שנאמר "וְלֹא תִקְחוּ כֹּפֶר לָנוּס אֶל עִיר מִקְלָטוֹ" (במדבר לה, לב).
Why · Sefer HaChinuch #413
Not to take ransom from one liable for exile to exempt him from exile
“The root of the prohibition to take ransom from one who kills inadvertently and all of its content is like the content of one who kills volitionally.”
Where in the Mishneh Torah
Hilchot Murderer and the Preservation of Life הלכות רוצח ושמירת נפש