Exodus 4:18-23

And Moses went and returned to Jethro his father-in-law, and said unto him, Let me go, I pray thee, and return unto my brethren that are in Egypt, and see whether they be yet alive. And Jethro said to Moses, Go in peace. And Jehovah said unto Moses in Midian, Go, return into Egypt; for all the men are dead that sought thy life. And Moses took his wife and his sons, and set them upon an ass, and he returned to the land of Egypt: and Moses took the rod of God in his hand. And Jehovah said unto Moses, When thou goest back into Egypt, see that thou do before Pharaoh all the wonders which I have put in thy hand: but I will harden his heart and he will not let the people go. And thou shalt say unto Pharaoh, Thus saith Jehovah, Israel is my son, my first-born: and I have said unto thee, Let my son go, that he may serve me; and thou hast refused to let him go: behold, I will slay thy son, thy first-born.