thou art my sister:

And there was a famine in the land: and Abram went down into Egypt to sojourn there; for the famine was grievous in the land. And it came to pass, when he was come near to enter into Egypt, that he said unto Sarai his wife, Behold now, I know that thou art a fair woman to look upon: Therefore it shall come to pass, when the Egyptians shall see thee, that they shall say, This is his wife: and they will kill me, but they will save thee alive. Say, I pray thee, thou art my sister: that it may be well with me for thy sake; and my soul shall live because of thee. And it came to pass, that, when Abram was come into Egypt, the Egyptians beheld the woman that she was very fair. Genesis 12:10-14 King James Bible