Charles Ellicott Commentary Genesis 18:9

"And they said unto him, Where is Sarah thy wife? And he said, Behold, in the tent." — Genesis 18:9 (ASV)

They said. But in Genesis 18:10, he said, and in Genesis 18:13, Genesis 18:17, Genesis 18:20, and other verses, the Lord (Jehovah) said. The messenger speaks as one with Jehovah, or as being His representative.

Where is Sarah your wife? This question is contrary to Middle Eastern customs, as women could only be referred to in the most indirect manner. But during the meal, as Abraham talked with the strangers, he had probably begun to recognize in them something more than human.