וַיֹּ֥אמֶר אֲבִימֶ֖לֶךְ אֶל־אַבְרָהָ֑ם מָ֣ה רָאִ֔יתָ כִּ֥י עָשִׂ֖יתָ אֶת־הַדָּבָ֥ר הַזֶּֽה׃
Abimèlech soggiunse ad Abramo: Che motivo avesti, per cui facesti questa cosa?
Or HaChaim on Genesis
ויאמר אבימלך. Avimelech said. Seeing that the previous verse had been a rebuke only, he now switched to a question. This is why the sentence had to begin once more with the words: "Avimelech said," though Abraham had not yet responded to the accusation. Avimelech now conceded that he did not consider Abraham capable of wanting to harm him intentionally.
Radak on Genesis
ויאמר, Avimelech wanted to know why Avraham had not personally protested the forced abduction of Sarah instead of allowing the king to become guilty of a greater crime. Surely a man such as he must have had a good reason for allowing this to happen without protest!?
Haamek Davar on Genesis
What did you see. What caused you to fear me? — The Philistines of those days were civilized and honorable.