Exodus 4:8-9

4:8 “If they do not believe you or pay attention to the former sign, then they may believe the latter sign. 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 4:15-16

4:15 “So you are to speak to him and put the words in his mouth. And as for me, I will be with your mouth and with his mouth, and I will teach you both what you must do. 4:16 He will speak for you to the people, and it will be as if he were your mouth and as if you were his God.