Exodus 8:15

8:15 But when Pharaoh saw that there was relief, he hardened his heart and did not listen to them, just as the Lord had predicted.

Exodus 8:31-32

8:31 and the Lord did as Moses asked – he removed the swarms of flies from Pharaoh, from his servants, and from his people. Not one remained! 8:32 But Pharaoh hardened his heart this time also and did not release the people.