Exodus 4:11-15

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.”

But he said, “Please, Lord, now send the message by whomever You will.” Aaron to Be Moses’ Mouthpiece

Then the anger of the Lord burned against Moses, and He said, “Is there not your brother Aaron the Levite? I know that he speaks fluently. And moreover, behold, he is coming out to meet you; when he sees you, he will be overjoyed.

So you are to speak to him and put the words in his mouth; and I Myself will be with your mouth and his mouth, and I will instruct you in what you are to do.