Exodus 7:5

Exo. 7:5. "The Egyptians shall know that I am the Lord, when I stretch forth My hand." The first time that Moses and Aaron went to Pharaoh, they told him that Jehovah, the God of Israel, commanded that he should let His people go, as in the beginning of chap. 5. Pharaoh then took it in great disdain to be told of such a command from Jehovah the God of Israel, a poor abject people, a company of slaves; and, by the character they bear, he concludes that He made no better figure among the gods than His people did among the nations. He makes answer, "Who is Jehovah, that I should obey His voice to let Israel go? I know not Jehovah." Jehovah was a hard name to him that he never heard of before, but he resolves that it shall be no bugbear to him. Jehovah! who is that? says Pharaoh in disdain. Now God tells Moses that He will make him know who He is - "He shall know that I am Jehovah when I stretch forth mine hand upon Egypt, and bring out the children of Israel from among them."