25 Then Pharaoh summoned Moses and Aaron, and said, “Go, sacrifice to your God within the land.” 26 But Moses said, “It would not be right to do so; for the sacrifices that we offer to the Lord our God are offensive to the Egyptians. If we offer in the sight of the Egyptians sacrifices that are offensive to them, will they not stone us? 27 We must go a three days’ journey into the wilderness and sacrifice to the Lord our God as he commands us.” 28 So Pharaoh said, “I will let you go to sacrifice to the Lord your God in the wilderness, provided you do not go very far away. Pray for me.” 29 Then Moses said, “As soon as I leave you, I will pray to the Lord that the swarms of flies may depart tomorrow from Pharaoh, from his officials, and from his people; only do not let Pharaoh again deal falsely by not letting the people go to sacrifice to the Lord.”

30 So Moses went out from Pharaoh and prayed to the Lord. 31 And the Lord did as Moses asked: he removed the swarms of flies from Pharaoh, from his officials, and from his people; not one remained. 32 But Pharaoh hardened his heart this time also, and would not let the people go.