skeptic bible source http://www.skepticsannotatedbible.com/gen/20.html
As noted in the skeptic bible source,
Abraham said of Sarah his wife, She is my sister."
Honest Abe does the same "she's my sister" routine again, for the same cowardly reason. And once again, the king just couldn't resist Sarah -- even though by now she is over 90 years old. (See Genesis 12:13-20 for the first, nearly identical, episode, and 26:7 for another repeat with Isaac, Rebekah and the same king Abimelech.)
The author of Genesis must run out of ideas and was recycling old stuff. Or was Abraham, who was previously called Abram, that good in using the same trick twice (and will be a third time as noted by skeptic bible)
The above point is only a digression, god and Abraham were engaged in a kind of extortion - deliberately putting Abimelech in a trap and god threatened Abimelech in order to extort "sheep and oxen and male and female servants..." Only upon praying to god by Abraham that god healed Abimelech and his wife and his maids, so that they bore children.
Oh, goodness! I can only hope that no intelligent human will take that book seriously and model our society using that as a moral reference.