Parashas Masei · Passuk 35:32 · TT note 1
Chabad.org — English translation + Rashi
Torah Temimah points to Kesuvos 37b (TT note on “וְלֹא תִקְחוּ כֹפֶר לָנוּס”).
English: You shall not take money from him and exempt him from exile.
No monetary commutation of the exile penalty.
Just as capital murder cannot be ransomed, so the unintentional killer cannot buy his way out of the city of refuge.