Exodus 4:16
Aaron will speak for you as a prophet speaks for his god.
and he will be glad when he sees you. You will speak to him and tell him what I have told you to say. And when you tell him or he speaks, I will be with you and teach you what you have to say.
At this, the Lord became angry with Moses and said: “What about your brother Aaron, the Levite? I know he speaks well. Look! He is coming to meet you,
The Lord said to him: “Who gave man a mouth? Who makes him dumb or deaf, with sight or blind? Is it not I, the Lord?
Moses said to the Lord: “But, my Lord, never have I been a fluent speaker before or after you have spoken to me. I cannot find words to express what I want to say.”
But if these two signs are not enough to make them believe you, take some water from the Nile and pour it on the ground, and the water from the river will turn into blood.”
The Lord added: “If they don’t believe you and are not convinced by the first sign, they will believe you when they see the second.
And God said: “Put your hand back on your chest.” So he put it back, and when he took it away again, his hand was healthy like the rest of his body.