Exodus 4:19-23

19Now the LORD had said to Moses in Midian, “Go back to Egypt, for all those who wanted to kill you are dead.”

20So Moses took his wife and sons, put them on a donkey and started back to Egypt. And he took the staff of God in his hand. 21The 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. 22Then say to Pharaoh, ‘This is what the LORD says: Israel is my firstborn son,

23and I told you, “Let my son go, so he may worship me.” But you refused to let him go; so I will kill your firstborn son.’ ”