Or HaChaim on Genesis 20:11/אור החיים על בראשית כ׳:י״א

1 בי אמרתי…אין יראת אלוקים במקום הזה. "For I said (to myself) that there is no fear of the Lord in this place." This is the answer to the question: "what did you see?" Abraham prefaced his answer with the word רק, "only." He wanted to forestall Avimelech saying to him that if he, Abraham, considered the men as lacking in basic fear of the Lord, why did he worry more about their murdering him and then taking his wife? He should have worried more about the latter! Abraham said: רק, i.e. "I reasoned that they would try and minimise their culpability. As long as I would be alive every man sleeping with my wife would commit a capital offence every time, and would accordingly face many punishments. If they killed me first, they would only be guilty of murder once, whereas they would not become culpable for sleeping with my widow. If a number of them would conspire to kill me, each one causing a single injury not in itself fatal, they would claim that they were not even guilty of murder." Abraham said that this was why he decided to describe Sarah as his sister.