Rashi on Exodus 32:26/רש"י על שמות ל״ב:כ״ו

1מי לה' אלי means, WHOEVER IS FOR THE LORD let him come TO ME.

2כל בני לוי ALL THE SONS OF LEVI — All the sons — from this we may gather that all the tribe of Levi remained worthy men (consequently “slay every man his brother” in the next verse can refer only to one who was his brother from the same mother, as explained by Rashi there) (Yoma 66b).