John Gill Commentary Genesis 20:10

"And Abimelech said unto Abraham, What sawest thou, that thou hast done this thing?" — Genesis 20:10 (ASV)

And Abimelech said to Abraham
Continuing his discourse with him: what you saw, that you have done this thing ?
he desires to know what he had observed, either in him or his people, that gave him any reason to conclude that they were a lustful people, and would stick at nothing to gratify their lusts, which put him upon taking such a method to secure his life, lest they should kill him for his wife's sake.