Exodus 7:15

12 For every one of them put down his rod on the earth, and they became snakes: but Aaron's rod made a meal of their rods.

13 But Pharaoh's heart was made hard, and he did not give ear to them, as the Lord had said.

14 And the Lord said to Moses and Aaron, Pharaoh's heart is unchanged; he will not let the people go.

15 Go to Pharaoh in the morning; when he goes out to the water, you will be waiting for him by the edge of the Nile, with the rod which was turned into a snake in your hand;

16 And say to him, The Lord, the God of the Hebrews, has sent me to you, saying, Let my people go so that they may give me worship in the waste land; but up to now you have not given ear to his words.

17 So the Lord says, By this you may be certain that I am the Lord; see, by the touch of this rod in my hand the waters of the Nile will be turned to blood;

18 And the fish in the Nile will come to destruction, and the river will send up a bad smell, and the Egyptians will not be able, for disgust, to make use of the water of the Nile for drinking.