Bereisheet (Genesis): Vayeira > Ch 20
Abraham travels to Gerar. Abimelech, king of Gerar, takes away Sarah thinking that she is Abraham’s sister
Abraham traveled south to Gerar. As before, he said that Sarah is his sister.
Abimelech the king of Gerar sent and took Sarah.
G-d saves Sarah and reunites her with Abraham
G-d came to Abimelech in a dream, and told him:
"Behold you are going to die because of the woman whom you have taken, for she is a married woman."
Abimelech had not come near to her and asked G-d not to kill him, as he is innocent. And G-d said to him in a dream,
"I too know that you did this with the innocence of your heart, and I too have withheld you from sinning to Me; therefore, I did not let you touch her. And now, return the man's wife, because he is a prophet, and he will pray for you and [you will] live; but if you do not return [her], know that you will surely die, you and all that is yours."
Abimelech returned Sarah to Abraham, gave him flocks and cattle and menservants and maidservants, and invited Abraham to dwell anywhere in his land.
Abraham told Abimelech that Sarah is the daughter of his father, but not the daughter of his mother.
Abraham prayed to G-d, and G-d healed Abimelech and his wife and his handmaids, and they gave birth. For the Lord had shut every womb of Abimelech's household, because of Sarah, Abraham's wife.
Here is my land before you
But Pharaoh said to him (above 12:19): “And now, here is your wife; take [her] and go,” because he was afraid, because the Egyptians were immersed in lewdness.
and he gave [them] to Abraham
in order to appease him so that he would pray for him.
my sister, the daughter of my father
Now if you ask: Was she not the daughter of his brother? The answer is that grandchildren are considered like children (Tosefta. Yev. 8:8, Talmud Bavli, Yev. 62b); therefore, she was (considered as) Terah’s daughter.