Exodus 4:15

12 Now therefore go, and I will be with thy mouth, and teach thee what thou shalt speak.

13 And he said, Oh, Lord, send, I pray thee, by the hand of him whom thou wilt send.

14 And the anger of Jehovah was kindled against Moses, and he said, Is there not Aaron thy brother the Levite? I know that he can speak well. And also, behold, he cometh forth to meet thee: and when he seeth thee, he will be glad in his heart.

15 And thou shalt speak unto him, and put the words in his mouth: and I will be with thy mouth, and with his mouth, and will teach you what ye shall do.

16 And he shall be thy spokesman unto the people; and it shall come to pass, that he shall be to thee a mouth, and thou shalt be to him as God.

17 And thou shalt take in thy hand this rod, wherewith thou shalt do the signs.

18 And Moses went and returned to Jethro his father-in-law, and said unto him, Let me go, I pray thee, and return unto my brethren that are in Egypt, and see whether they be yet alive. And Jethro said to Moses, Go in peace.