Exodus 4:8-12

“So if they will not believe you nor pay attention to the evidence of the first sign, they may believe the evidence of the last sign.

But if they will not believe even these two signs nor pay attention to 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 will turn into blood on the dry ground.”

Then Moses said to the Lord, “Please, Lord, I have never been eloquent, neither recently nor in time past, nor since You have spoken to Your servant; for I am slow of speech and slow of tongue.”

But the Lord said to him, “Who has made the human mouth? Or who makes anyone unable to speak or deaf, or able to see or blind? Is it not I, the Lord?

Now then go, and I Myself will be with your mouth, and instruct you in what you are to say.”