Exodus 8:19

15 When Pharaoh saw that there was relief, however, he hardened his heart and would not listen to Moses and Aaron, just as the LORD had said.

16 Then the LORD said to Moses, “Tell Aaron, ‘Stretch out your staff and strike the dust of the earth, that it may turn into swarms of gnats throughout the land of Egypt.’”

17 This they did, and when Aaron stretched out his hand with his staff and struck the dust of the earth, gnats came upon man and beast. All the dust of the earth turned into gnats throughout the land of Egypt.

18 The magicians tried to produce gnats using their magic arts, but they could not. And the gnats remained on man and beast.

19 “This is the finger of God,” the magicians said to Pharaoh. But Pharaoh’s heart was hardened, and he would not listen to them, just as the LORD had said.

20 Then the LORD said to Moses, “Get up early in the morning, and when Pharaoh goes out to the water, stand before him and tell him that this is what the LORD says: ‘Let My people go, so that they may worship Me.

21 But if you will not let My people go, I will send swarms of flies upon you and your officials and your people and your houses. The houses of the Egyptians and even the ground where they stand will be full of flies.

22 But on that day I will give special treatment to the land of Goshen, where My people live; no swarms of flies will be found there. In this way you will know that I, the LORD, am in the land.

23 I will make a distinction between My people and your people. This sign will take place tomorrow.’”

Read all of Exodus 8