Genesis 12:11-13

And when he was near to enter into Egypt, he said to Sarai his wife: I know that thou art a beautiful woman:

And that when the Egyptians shall see thee, they will say: She is his wife: and they will kill me, and keep thee.

Say, therefore, I pray thee, that thou art my sister: that I may be well used for thee, and that my soul may live for thy sake.