Rashi on Numbers
נכה בו (this may mean, “we may smite them”) I and my people may smite them. — Another explanation is that this is a Mishnaic Hebrew expression as in (Bava Metzia 105b) “he deducts (מנכה) for him something from the price”, so that it means: [perhaps I may be able] to reduce them a little in numbers (Midrash Tanchuma, Balak 4).
Ramban on Numbers
THAT WE MAY SMITE THEM — the meaning [of the plural “we,” although it is only Balaam who is speaking], is “I and Midian my ally.”31This is unlike Rashi, who explains the plural “we” as meaning “I and my people.”