Exodus 7:14-16

14And Jehovah said to Moses, Pharaoh's heart is hardened: he refuseth to let the people go.

15Go unto Pharaoh in the morning — behold, he will go out unto the water — and take thy stand by the bank of the river in front of him; and take in thy hand the staff that was turned into a serpent.

16And say unto him, Jehovah the 1God of the Hebrews has sent me to thee, saying, Let my people go, that they may serve me in the wilderness; but behold, hitherto thou hast not hearkened.