Exodus 4:19-23
New Revised Standard Version (NRSV)

19 The Lord said to Moses in Midian, “Go back to Egypt; for all those who were seeking your life are dead.” 20 So Moses took his wife and his sons, put them on a donkey, and went back to the land of Egypt; and Moses carried the staff of God in his hand.

21 And the Lord said to Moses, “When you go back to Egypt, see that you perform before Pharaoh all the wonders that I have put in your power; but I will harden his heart, so that he will not let the people go. 22 Then you shall say to Pharaoh, ‘Thus says the Lord: Israel is my firstborn son. 23 I said to you, “Let my son go that he may worship me.” But you refused to let him go; now I will kill your firstborn son.’”