Exodus 8:23-25

King James Version

²³ And I will put a division between my people and thy people: to morrow shall this sign be.

²⁴ And the Lord did so; and there came a grievous swarm of flies into the house of Pharaoh, and into his servants' houses, and into all the land of Egypt: the land was corrupted by reason of the swarm of flies.

²⁵ And Pharaoh called for Moses and for Aaron, and said, Go ye, sacrifice to your God in the land.