Shemot 4:21-23

Orthodox Jewish Bible

²¹ And Hashem said unto Moshe, When thou goest to return into Mitzrayim, see that thou do all those mofetim before Pharaoh, which I have put in thine yad: but I will harden his lev, that he shall not let HaAm go.

²² And thou shalt say unto Pharaoh, Thus saith Hashem, Yisroel is beni (My son), even My bechor (first-born):

²³ And I say unto thee, Let beni (My son) go, that he may serve Me: and if thou refuse to let him go, hinei, I will slay thy ben, even thy bechor.