Exodus 4:21 in the King James Version
And the LORD said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go.
Context
20 Moses took his wife and his sons, and set them on a donkey, and he returned to the land of Egypt. Moses took God’s rod in his hand.
21 The LORD said to Moses, “When you go back into Egypt, see that you do before Pharaoh all the wonders which I have put in your hand, but I will harden his heart and he will not let the people go.
22 You shall tell Pharaoh, ‘The LORD says, Israel is my son, my firstborn,