וַתָּבֹ֤א בַת־שֶׁ֙בַע֙ אֶל־הַמֶּ֣לֶךְ שְׁלֹמֹ֔ה לְדַבֶּר־ל֖וֹ עַל־אֲדֹנִיָּ֑הוּ וַיָּקָם֩ הַמֶּ֨לֶךְ לִקְרָאתָ֜הּ וַיִּשְׁתַּ֣חוּ לָ֗הּ וַיֵּ֙שֶׁב֙ עַל־כִּסְא֔וֹ וַיָּ֤שֶׂם כִּסֵּא֙ לְאֵ֣ם הַמֶּ֔לֶךְ וַתֵּ֖שֶׁב לִֽימִינֽוֹ׃
Bath-sheba therefore went unto king Solomon, to speak unto him for Adonijah. And the king rose up to meet her, and bowed down unto her, and sat down on his throne, and caused a throne to be set for the king’s mother; and she sat on his right hand.
Rashi
אל אשר דברתי לך OF WHICH I HAVE SPOKEN UNTO THEE — Here we have an instance of לך connected with the verb דבר being used in place of אליך (i. e. where לך actually means speaking to, not as its usual meaning it, speaking “concerning” someone or “in the interest of” someone as often pointed out by Rashi; cf. e. g., Rashi’s comment on Genesis 28:15). Similar is, (1 Kings 2:19) “to speak unto him (לדבר לו) for Adonijah” (cf. Rashi on that verse).
Siftei Chakhamim
Here is an instance where לך is used connected with the verb דבור in the place of אליך . . . Explanation: לי , לך and להם , when following דבור , usually mean “about me,” “about you” and “about them,” [rather than “to me,” “to you” and “to them”]. This was explained in Bereishis 24:7. Nevertheless, לך here means “to you.” [Rashi knows this] because nowhere does it say that God spoke to someone else “about” Moshe. And so with [ לדבר לו ] written about Adoniyahu (Melachim I 2:19). There too it means “to him,” not “about him.”