Exodus 4:15

12 So go now, and I will be with your mouth, teaching you what to say.

13 And he said, O Lord, send, if you will, by the hand of anyone whom it seems good to you to send.

14 And the Lord was angry with Moses, and said, Is there not Aaron, your brother, the Levite? To my knowledge he is good at talking. And now he is coming out to you: and when he sees you he will be glad in his heart.

15 Let him give ear to your voice, and you will put my words in his mouth; and I will be with your mouth and with his, teaching you what you have to do.

16 And he will do the talking for you to the people: he will be to you as a mouth and you will be to him as God.

17 And take in your hand this rod with which you will do the signs.

18 And Moses went back to Jethro, his father-in-law, and said to him, Let me go back now to my relations in Egypt and see if they are still living. And Jethro said to Moses, Go in peace.