Exodus 8:20-24

20And Jehovah said to Moses, Rise up early in the morning, and stand before Pharaoh — behold, he will go out to the water — and say to him, Thus saith Jehovah, Let my people go, that they may serve me.

21For, if thou do not let my people go, behold, I will send dog-flies upon thee, and upon thy bondmen, and upon thy people, and into thy houses; and the houses of the Egyptians shall be full of dog-flies, and also the ground on which they are.

22And I will distinguish in that day the land of Goshen, in which my people dwell, that no dog-flies shall be there; that thou mayest know that I Jehovah am in the midst of the land.

23And I will put a separation between my people and thy people; to-morrow shall this sign be.

24And Jehovah did so; and there came dog-flies in a multitude into the house of Pharaoh, and [into] the houses of his bondmen; and throughout the land of Egypt, the land was corrupted by the dog-flies.