Exodus 4:23

And I said to thee, Send away my people, that they may serve me: now if thou wilt not send them away, see, I will slay thy first-born son.

And I say unto thee, Let my son go, that he may serve me: and if thou refuse to let him go, behold, I will slay thy son, even thy firstborn.

and I have said to you, “Let my son go, that he may serve me;” and you have refused to let him go. Behold, I will kill your firstborn son.’”