John Gill Commentary Genesis 18:13

"And Jehovah said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, who am old?" — Genesis 18:13 (ASV)

And the Lord said to Abraham
This discovers who the person was that had been conversing with Abraham, that he was a divine Person, as appears by his name "Jehovah", as well as by his knowledge of Sarah's behaviour; he did not turn himself to her, that it might be more manifest that it was not upon the sight of her he judged she laughed, but from his own omniscience; and he chose rather to speak to her husband than to her, appearing as a stranger, and that he might reprove her: why did Sarah laugh, saying, shall I of a surety bear a child ,
which am old ?
suggesting there was no reason for it, and signifying his displeasure and indignation at it.