Exodus 11:9
Then the LORD said to Moses, "Pharaoh will not listen to you, that my wonders may be multiplied in the land of Egypt."
Exodus 7:3-4
But I will harden Pharaoh's heart, and though I multiply my signs and wonders in the land of Egypt,
Exodus 3:19
But I know that the king of Egypt will not let you go unless compelled by a mighty hand.
Exodus 10:1
Then the LORD said to Moses, "Go in to Pharaoh, for I have hardened his heart and the heart of his servants, that I may show these signs of mine among them,
Romans 9:16-18
So then it depends not on human will or exertion, but on God, who has mercy.