Exodus 4:21-23

New International Version - UK

²¹ The Lord said to Moses, ‘When you return to Egypt, see that you perform before Pharaoh all the wonders I have given you the power to do. But I will harden his heart so that he will not let the people go. ²² Then say to Pharaoh, “This is what the Lord says: Israel is my firstborn son, ²³ and I told you, ‘Let my son go, so that he may worship me.’ But you refused to let him go; so I will kill your firstborn son.”’