Exodus 4:14-15
4:14 Then the Lord became angry with Moses, and he said, “What about your brother Aaron the Levite? I know that he can speak very well. Moreover, he is coming to meet you, and when he sees you he will be glad in his heart.
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.