Exodus 8:28-32

28Pharaoh 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.”

29“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.”

30Then Moses left Pharaoh’s presence and appealed to the Lord.

31The Lord did as Moses had said: He removed the swarms of flies from Pharaoh, his officials, and his people; not one was left.

32But Pharaoh hardened his heart this time also and did not let the people go.