Exodus 8:10; Exodus 7:17

10 And he said, Tomorrow. Moses said, Be it as you say, so wthat you may know that xthere is no one like the Lord our God.

17 Thus says the Lord, By this dyou 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 eit shall turn into blood.