Genesis 12:11-13

11And 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:

12Therefore 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.

13Say, 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.