The Lord said to Moses, "Get up early in the morning and present yourself to Pharaoh when you see him going out to the water. Tell him: This is what the Lord says: Let My people go, so that they may worship Me.
But if you will not let My people go, then I will send swarms of flies against you, your officials, your people, and your houses. The Egyptians' houses will swarm with flies, and so will the land where they live.
But on that day I will give special treatment to the land of Goshen, where My people are living; no flies will be there. This way you will know that I, the Lord, am in the land.
I will make a distinction between My people and your people. This sign will take place tomorrow."
And the Lord did this. Thick swarms of flies went into Pharaoh's palace and his officials' houses. Throughout Egypt the land was ruined because of the swarms of flies.
Then Pharaoh summoned Moses and Aaron and said, "Go sacrifice to your God within the country."
But Moses said, "It would not be right to do that, because what we will sacrifice to the Lord our God is detestable to the Egyptians. If we sacrifice what the Egyptians detest in front of them, won't they stone us?
We must go a distance of three days into the wilderness and sacrifice to the Lord our God as He instructs us."
Pharaoh responded, "I will let you go and sacrifice to the Lord your God in the wilderness, but don't go very far. Make an appeal for me."
"As soon as I leave you," Moses said, "I will appeal to the Lord, and tomorrow the swarms of flies will depart from Pharaoh, his officials, and his people. But Pharaoh must not act deceptively again by refusing to let the people go and sacrifice to the Lord."
Then Moses left Pharaoh's presence and appealed to the Lord.
The Lord did as Moses had said: He removed the swarms of flies from Pharaoh, his officials, and his people; not one was left.
But Pharaoh hardened his heart this time also and did not let the people go.