Genesis 12:11-13

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:

When he was come near to enter into Egypt, that he said unto Sarai his wife. On reaching the confines of Egypt, which was the greatest primeval kingdom of the world, he began to feel uneasy. Increasing signs of civilization, grandeur, and power, met his eye on every side; and as the immigration of so numerous a tribe as his from the neighbouring desert would certainly arrest public attention, the prospect of encountering the authorities of Egypt, so different from the simple nomads of Asia, to whom his experience had hitherto been limited, filled him with awe. But all other anxieties were forgotten and absorbed in one cause of alarm.

I know that thou art a fair woman. Sarai's complexion, coming from a mountainous country, would be fresh and fair compared with the faces of Egyptian women, which, as the monuments show, were dark-brown or copper-coloured. He entertained a bad opinion of the morals and manners of the country; and anticipating that Sarai, whose style of beauty was far superior to that of the Egyptian women, might captivate some proud noble, who would try by any means to obtain possession of her, Abram became apprehensive of his life.

The idea so completely unnerved him that his fortitude and faith alike gave way; and he formed an artful plan, which, while it would retain his wife beside him, would, he hoped, by leading to betrothal and other negotiations connected with the dowry, put off the evil day. The counsel of Abram to Sarai was true in words; but it was a deception, intended to give an impression that she was no more than his sister. His conduct was culpable and inconsistent with his character as a servant of God; it showed a reliance on worldly policy more than a trust in the promise; and he not only sinned himself, but tempted Sarai to sin also.