Exodus 8:12

8:12 Then Moses and Aaron went out from Pharaoh, and Moses cried to the Lord because of the frogs that he had brought on Pharaoh.

Exodus 8:19

8:19 The magicians said to Pharaoh, “It is the finger of God!” But Pharaoh’s heart remained hard, and he did not listen to them, just as the Lord had predicted.

Exodus 9:7

9:7 Pharaoh sent representatives to investigate, and indeed, not even one of the livestock of Israel had died. But Pharaoh’s heart remained hard, and he did not release the people.

Exodus 14:4

14:4 I will harden Pharaoh’s heart, and he will chase after them. I will gain honor because of Pharaoh and because of all his army, and the Egyptians will know that I am the Lord.” So this is what they did.