Exodus 7:15-18

15Go to Pharaoh in the morning, as he is going out to the water. Stand on the bank of the Nile to meet him, and take in your hand the staff that turned into a serpent.

16And you shall say to him, 'The Lord, the God of the Hebrews, sent me to you, saying, "Let my people go, that they may serve me in the wilderness." But so far, you have not obeyed.

17Thus says the Lord, "By this you shall know that I am the Lord: behold, with the staff that is in my hand I will strike the water that is in the Nile, and it shall turn into blood.

18The fish in the Nile shall die, and the Nile will stink, and the Egyptians will grow weary of drinking water from the Nile."'"