The LORD instructed Moses, “When you go back to Egypt, see that you perform before Pharaoh all the wonders that I have put within your power. But I will harden his heart so that he will not let the people go.
Jewish Publication Society of America Version (JPS1917) - Exodus 4:21 >And the LORD said unto Moses: 'When thou goest back into Egypt, see that thou do before Pharaoh all the wonders which I have put in thy hand; but I will harden his heart, and he will not let the people go.