Exodus 4:18-23

18And Moses went and returned to Jethro his father in law, and said to him, Let me go, I pray thee, and return to my brethren who are in Egypt, and see whether they are yet alive. And Jethro said to Moses, Go in peace.1 19And the LORD said to Moses in Midian, Go, return into Egypt: for all the men are dead who sought thy life. 20And Moses took his wife and his sons, and set them upon a donkey, and he returned to the land of Egypt: and Moses took the rod of God in his hand. 21And the LORD said to Moses, When thou goest to return into Egypt, see that thou perform all those wonders before Pharaoh, which I have put in thy hand: but I will harden his heart, that he shall not let the people go. 22And thou shalt say to Pharaoh, Thus saith the LORD, Israel is my son, even my firstborn: 23And I say to thee, Let my son go, that he may serve me: and if thou shalt refuse to let him go, behold, I will slay thy son, even thy firstborn.