Exodus 7:5

7:5 Then the Egyptians will know that I am the Lord, when I extend my hand over Egypt and bring the Israelites out from among them.

Exodus 7:17

7:17 Thus says the Lord: “By this you will know that I am the Lord: I am going to strike the water of the Nile with the staff that is in my hand, and it will be turned into blood.