Exodus 8:22-26

And I will sever in that day the land of Goshen, in which my people dwell, that no swarms of flies shall be there; to the end thou mayest know that I am the LORD in the midst of the earth.

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

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.

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

And Moses said, It is not meet so to do; for we shall sacrifice the abomination of the Egyptians to the LORD our God: lo, shall we sacrifice the abomination of the Egyptians before their eyes, and will they not stone us?