Exodus 8:20-24

Then the LORD said to Moses, “Get up early in the morning and confront Pharaoh as he goes to the river and say to him, ‘This is what the LORD says: Let my people go, so that they may worship me. If you do not let my people go, I will send swarms of flies on you and your officials, on your people and into your houses. The houses of the Egyptians will be full of flies; even the ground will be covered with them. “ ‘But on that day I will deal differently with the land of Goshen, where my people live; no swarms of flies will be there, so that you will know that I, the LORD, am in this land. I will make a distinction between my people and your people. This sign will occur tomorrow.’ ” And the LORD did this. Dense swarms of flies poured into Pharaoh’s palace and into the houses of his officials; throughout Egypt the land was ruined by the flies.