Exodus 10:20 in the King James Version
But the LORD hardened Pharaoh’s heart, so that he would not let the children of Israel go.
Context
19 The 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.
20 But the LORD hardened Pharaoh’s heart, and he didn’t let the children of Israel go.
21 The 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.”