Exodus 4:8-9

8“If they will not believe you or 1heed the 2witness of the first sign, they may believe the 3witness of the last sign. 9But if they will not believe even these two signs or heed what you say, then you shall take some water from the Nile and pour it on the dry ground; and the water which you take from the Nile 4will become blood on the dry ground.”