Exod 7:13 Yet Pharaoh's heart was hardened, and he did not listen to them, as the LORD had said.
Exod 7:22 But the magicians of Egypt did the same with their secret arts; and Pharaoh's heart was hardened, and he did not listen to them, as the LORD had said.
Exod 8:15 But when Pharaoh saw that there was relief, he hardened his heart and did not listen to them, as the LORD had said.
Exod 8:19 Then the magicians said to Pharaoh, "This is the finger of God." But Pharaoh's heart was hardened, and he did not listen to them, as the LORD had said.
Exod 8:32 But Pharaoh hardened his heart this time also, and he did not let the people go.
Exod 9:7 Pharaoh sent, and behold, there was not even one of the livestock of Israel dead. But the heart of Pharaoh was hardened, and he did not let the people go.
...but finally.
Exod 9:12 And the LORD hardened Pharaoh's heart, and he did not listen to them, just as the LORD had spoken to Moses.