Exodus 7:14-16

14And Yhwh said unto Moses, Pharaoh’s heart is hardened, he refuseth to let the people go. 15Get thee unto Pharaoh in the morning; lo, he goeth out unto the water; and thou shalt stand by the river’s brink against he come; and the rod which was turned to a serpent shalt thou take in thine hand. 16And thou shalt say unto him, Yhwh God of the Hebrews hath sent me unto thee, saying, Let my people go, that they may serve me in the wilderness: and, behold, hitherto thou wouldest not hear.