Exodus 4:9

4:9 And if they do not believe even these two signs or listen to you, then take some water from the Nile and pour it out on the dry ground. The water you take out of the Nile will become blood on the dry ground.”

Exodus 10:2

10:2 and in order that in the hearing of your son and your grandson you may tell how I made fools of the Egyptians and about my signs that I displayed among them, so that you may know that I am the Lord.”