Exodus 4:11

“It will happen, if they will not believe you or listen to the voice of the first sign, that they will believe the voice of the latter sign.

It will happen, if they will not believe even these two signs or listen to your voice, that you shall take of the water of the river, and pour it on the dry land. The water which you take out of the river will become blood on the dry land.”

Moses said to the LORD, “O Lord, I am not eloquent, neither before now, nor since you have spoken to your servant; for I am slow of speech, and of a slow tongue.”

Now therefore go, and I will be with your mouth, and teach you what you shall speak.”

Moses said, “Oh, Lord, please send someone else.”

The LORD’s anger burned against Moses, and he said, “What about Aaron, your brother, the Levite? I know that he can speak well. Also, behold, he is coming out to meet you. When he sees you, he will be glad in his heart.