Exodus 4:10

4:10 Then Moses said to the Lord, “O my Lord, I am not an eloquent man, neither in the past nor since you have spoken to your servant, for I am slow of speech and slow of tongue.”

Exodus 4:14

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.