Exodus 11:4-10 RSV

4 And Moses said, "Thus says the LORD: About midnight I will go forth in the midst of Egypt;
5 and all the first-born in the land of Egypt shall die, from the first-born of Pharaoh who sits upon his throne, even to the first-born of the maidservant who is behind the mill; and all the first-born of the cattle.
6 And there shall be a great cry throughout all the land of Egypt, such as there has never been, nor ever shall be again.
7 But against any of the people of Israel, either man or beast, not a dog shall growl; that you may know that the LORD makes a distinction between the Egyptians and Israel.
8 And all these your servants shall come down to me, and bow down to me, saying, 'Get you out, and all the people who follow you.' And after that I will go out." And he went out from Pharaoh in hot anger.
9 Then the LORD said to Moses, "Pharaoh will not listen to you; that my wonders may be multiplied in the land of Egypt."
10 Moses and Aaron did all these wonders before Pharaoh; and the LORD hardened Pharaoh's heart, and he did not let the people of Israel go out of his land.