Exodus 8:24-32 ESV
And the LORD did so. There came great swarms of flies into the house of Pharaoh and into his servants’ houses. Throughout all the land of Egypt the land was ruined by the swarms of flies.
Then Pharaoh called Moses and Aaron and said, “Go, sacrifice to your God within the land.” But Moses said, “It would not be right to do so, for the offerings we shall sacrifice to the LORD our God are an abomination to the Egyptians. If we sacrifice offerings abominable to the Egyptians before their eyes, will they not stone us? We must go three days’ journey into the wilderness and sacrifice to the LORD our God as he tells us.” So Pharaoh said, “I will let you go to sacrifice to the LORD your God in the wilderness; only you must not go very far away. Plead for me.” Then Moses said, “Behold, I am going out from you and I will plead with the LORD that the swarms of flies may depart from Pharaoh, from his servants, and from his people, tomorrow. Only let not Pharaoh cheat again by not letting the people go to sacrifice to the LORD.” So Moses went out from Pharaoh and prayed to the LORD. And the LORD did as Moses asked, and removed the swarms of flies from Pharaoh, from his servants, and from his people; not one remained. But Pharaoh hardened his heart this time also, and did not let the people go.
ESV: English Standard Version 2016