Numbers 24:3

בנו בער — The grammatical form בנו is exactly like that in (Psalms 114:8) “To a spring of (מעינו) water” (see Rashi on Numbers 23:18). But a Midrashic statement is: Both of them (Balak and Balaam) were superior to their fathers, for it states (Numbers 23:18): “Balak — his son was Zippor”, i.e. that his father (Zippor) was his son (his inferior) in respect to royalty, and Balaam was greater than his father in prophecy (because it states here, בלעם בנו בעור i.e. Balaam — his son was Beor): he was, so to speak, a Maneh, son of a Half-Maneh (Sanhedrin 105a, Midrash Tanchuma, Balak 13, cf. Taanit 28b). שתום העין WITH THE PENETRATING EYE — his eye was bored out and had been extracted and its eye socket could be seen to be open. The word שתום used in the sense of “boring a hole” is a Mishnaic usage: sufficient time that we can bore a hole (ישתום) in the cask and stop it up, and it (the clay of which the stopper is made) can dry (Avodah Zarah 69a). And our Rabbis said, Because he had said, (Numbers 23:10) ומספר את רבע ישראל, meaning that the Holy One, blessed be He, occupies Himself with counting the issue of the marital life of the Israelites, awaiting the time when a righteous man will be born, he therefore said to himself, “Does He who is holy and whose ministers are holy direct his mind to matters such as these?” On this account Balaam’s eye was blinded (Niddah 31a). But some explain that שתום העין means “open-eyed”, just as Onkelos translated (“who can see well”). And since it says, שתום העין "with an open eye” and it does not say, “with open eyes”, we may learn that in one of his eyes he was blind (Sanhedrin 105a).

וַיִּשָּׂ֥א מְשָׁל֖וֹ וַיֹּאמַ֑ר נְאֻ֤ם בִּלְעָם֙ בְּנ֣וֹ בְעֹ֔ר וּנְאֻ֥ם הַגֶּ֖בֶר שְׁתֻ֥ם הָעָֽיִן׃

And he took up his discourse, and said, The speech of Bil῾am the son Be῾or, and the speech of the man whose eyes are open: