Exodus 8:15, 19, 32

But when Pharaoh saw that there was respite, he hardened his heart, and hearkened not unto them, as Jehovah had spoken.

Then the magicians said unto Pharaoh, This is the finger of God: and Pharaoh’s heart was hardened, and he hearkened not unto them; as Jehovah had spoken.

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