Exodus 4:12

Now therefore go, and I will be with thy mouth
And put words into it, and cause it to speak readily and powerfully; and so it appears that he was mighty in words, as well as in deeds, ( Acts 7:22 ) : and teach thee what thou shalt say;
to Pharaoh, to the Israelites, and to Aaron, that was to speak for him, as is hereafter observed.