Exodus 8:28-32

28And Pharaoh said, I will let you go, that ye may sacrifice to Jehovah your God in the wilderness; only ye shall not go very far away: entreat for me. 29And Moses said, Behold, I go out from thee, and I will entreat Jehovah that the swarms of flies may depart from Pharaoh, from his servants, and from his people, to-morrow: only let not Pharaoh deal deceitfully any more in not letting the people go to sacrifice to Jehovah. 30And Moses went out from Pharaoh, and entreated Jehovah. 31And Jehovah did according to the word of Moses; and he removed the swarms of flies from Pharaoh, from his servants, and from his people; there remained not one. 32And Pharaoh hardened his heart this time also, and he did not let the people go.