Exodus 8:28-32

28So Pharaoh said, “I will let you go, so that you may sacrifice to the Lord your God in the wilderness; only you shall not go very far away. Plead [with your God] for me.”

29Moses said, “I am going to leave you, and I will urgently petition (pray, entreat) the Lord that the swarms of insects may leave Pharaoh, his servants, and his people tomorrow; only do not let Pharaoh act deceitfully again by not letting the people go to sacrifice to the Lord.”

30So Moses left Pharaoh and prayed to the Lord [on behalf of Pharaoh].

31The Lord did as Moses asked, and removed the swarms of [bloodsucking] insects from Pharaoh, from his servants and from his people; not one remained.

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