Exodus 6:29

And the Lord spake unto Moses, saying, I am the Lord
See ( Exodus 6:2 Exodus 6:6 Exodus 6:8 ) : speak thou unto Pharaoh king of Egypt all that I say unto thee;
that he let Israel go; and that in case of refusal, that he would punish him and his people with this and the other plague, one after another, and at last slay him and their firstborn.