Exodus 4:11 (KJV)

And it shall come to pass, if they will not believe also these two signs, neither hearken unto thy voice, that thou shalt take of the water of the river, and pour it upon the dry land: and the water which thou takest out of the river shall become blood upon the dry land.

And Moses said unto the Lord, O my Lord, I am not eloquent, neither heretofore, nor since thou hast spoken unto thy servant: but I am slow of speech, and of a slow tongue.

And the Lord said unto him, Who hath made man’s mouth? or who maketh the dumb, or deaf, or the seeing, or the blind? have not I the Lord?

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

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