Exodus 4:21-23

American Standard Version

²¹ 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 ^[a]harden his heart, and he will not let the people go. ²² And thou shalt say unto Pharaoh, Thus saith Jehovah, Israel is my son, my first-born: ²³ 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.