Exodus 10:20

18Moses went out from Pharaoh, and prayed to the LORD.

19The LORD sent an exceedingly strong west wind, which took up the locusts, and drove them into the Red Sea. There remained not one locust in all the borders of Egypt.

20But the LORD hardened Pharaoh’s heart, and he didn’t let the children of Israel go.

21The LORD said to Moses, “Stretch out your hand toward the sky, that there may be darkness over the land of Egypt, even darkness which may be felt.”

22Moses stretched out his hand toward the sky, and there was a thick darkness in all the land of Egypt for three days.