Exodus 4:21-24

²¹ And the Lord said to Moses, "When you go back to Egypt, see that you do all those wonders before Pharaoh which I have put in your hand. 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 son, My firstborn. ²³ So I say to you, let My son go that he may serve Me. But if you refuse to let him go, indeed I will kill your son, your firstborn." ' "

²⁴ And it came to pass on the way, at the encampment, that the Lord met him and sought to kill him.