Exodus 8:27-32

27 We must go three days' journey into the wilderness and sacrifice to the LORD our God as he will command us."
28 So Pharaoh said, "I will let you go, to sacrifice to the LORD your God in the wilderness; only you shall not go very far away. Make entreaty for me."
29 Then Moses said, "Behold, I am going out from you and I will pray to the LORD that the swarms of flies may depart from Pharaoh, from his servants, and from his people, tomorrow; only let not Pharaoh deal falsely again 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, and removed the swarms of flies from Pharaoh, from his servants, and from his people; not one remained.
32 But Pharaoh hardened his heart this time also, and did not let the people go.
Revised Standard Version of the Bible, copyright 1952 [2nd edition, 1971] by the Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved.