A Wife Introduced As A Sister

Genesis 12:10-16

10  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. 
11  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: 
12  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. 
13  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. 
14  And it came to pass, that, when Abram was come into Egypt, the Egyptians beheld the woman that she was very fair. 
15  The princes also of Pharaoh saw her, and commended her before Pharaoh: and the woman was taken into Pharaoh's house. 
16  And he entreated Abram well for her sake: and he had sheep, and oxen, and he asses, and menservants, and maidservants, and she asses, and camels.