Exodus 4:21-23

New Century Version

²¹ The Lord said to Moses, “When you get back to Egypt, do all the miracles I have given you the power to do. Show them to the king of Egypt. But I will make the king very stubborn, and he will not let the people go. ²² Then say to the king, ‘This is what the Lord says: Israel is my firstborn son. ²³ I told you to let my son go so he may worship me. But you refused to let Israel go, so I will kill your firstborn son.’”