Exodus 11:8-12

And all these thy servants shall come down unto me, and bow down themselves unto me, saying, Get thee out, and all the people that follow thee: and after that I will go out. And he went out from Pharaoh in a great anger.

And the LORD said unto Moses, Pharaoh shall not hearken unto you; that my wonders may be multiplied in the land of Egypt.

And Moses and Aaron did all these wonders before Pharaoh: and the LORD hardened Pharaoh’s heart, so that he would not let the children of Israel go out of his land.