Exodus 7:13-17
English Standard Version
Chapter 7
13Still Pharaoh 's heart was hardened, and he would not listen to them, as the Lord had said.
14Then the Lord said to Moses, "Pharaoh 's heart is hardened; he refuses to let the people go.
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.