Exodus 11:8-12

And all these servants of yours will come down to me and bow themselves before me, saying, ‘Go out, you and all the people who follow you,’ and after that I will go out.” And he left Pharaoh in the heat of anger.

Then the Lord said to Moses, “Pharaoh will not listen to you, so that My wonders will be multiplied in the land of Egypt.”

So Moses and Aaron performed all these wonders before Pharaoh; yet the Lord hardened Pharaoh’s heart, and he did not let the sons of Israel go out of his land.