Exodus 8:20-24

20Then the Lord told Moses, “Get up early in the morning and stand in Pharaoh’s way as he goes down to the river. Say to him, ‘This is what the Lord says: Let my people go, so they can worship me.

21If you refuse, then I will send swarms of flies on you, your officials, your people, and all the houses. The Egyptian homes will be filled with flies, and the ground will be covered with them.

22But this time I will spare the region of Goshen, where my people live. No flies will be found there. Then you will know that I am the Lord and that I am present even in the heart of your land.

23I will make a clear distinction between my people and your people. This miraculous sign will happen tomorrow.’”

24And the Lord did just as he had said. A thick swarm of flies filled Pharaoh’s palace and the houses of his officials. The whole land of Egypt was thrown into chaos by the flies.