Genesis 12:13
11 As he approached Egypt, he said to his wife Sarai, “Look, I know that you are a beautiful woman. 12 When the Egyptians see you they will say, ‘This is his wife.’ Then they will kill me but will keep you alive. 13 So tell them you are my sister so that it may go well for me because of you and my life will be spared on account of you.” 14 When Abram entered Egypt, the Egyptians saw that the woman was very beautiful.
Genesis 20:2
1 Abraham journeyed from there to the Negev region and settled between Kadesh and Shur. While he lived as a temporary resident in Gerar, 2 Abraham said about his wife Sarah, “She is my sister.” So Abimelech, king of Gerar, sent for Sarah and took her. 3 But God appeared to Abimelech in a dream at night and said to him, “You are as good as dead because of the woman you have taken, for she is someone else’s wife.”
Genesis 26:7
5 All this will come to pass because Abraham obeyed me and kept my charge, my commandments, my statutes, and my laws.” 6 So Isaac settled in Gerar. 7 When the men of that place asked him about his wife, he replied, “She is my sister.” He was afraid to say, “She is my wife,” for he thought to himself, “The men of this place will kill me to get Rebekah because she is very beautiful.” 8 After Isaac had been there a long time, Abimelech king of the Philistines happened to look out a window and observed Isaac caressing his wife Rebekah.
Notes and References
"... There are three stories in Genesis in which a patriarch’s wife is represented to be his sister, a king learns that she is actually the patriarch’s wife, and then the husband and wife leave and prosper: Genesis 12:10-20 (J); 20:1-18 (E); and 26:6-14 (J). The first and third are both J. They do not overlap characters: the first story is about Abraham-Sarah-Pharaoh; the second is about Isaac-Rebekah-Abimelec. The second story combines characters from each of the other two: Abraham-Sarah-Abimelec. The first and third stories use the name YHWH. The second story just says “God” ..."
Friedman, Richard Elliott The Bible with Sources Revealed: A New View Into the Five Books of Moses (p. 51) Harper San Francisco, 2005