Exodus 4:11

8 And it shall come to pass, if they will not believe thee, neither hearken to the voice of the first sign, that they will believe the voice of the latter sign.

9 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].

10 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.

11 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?

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

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

14 And the anger of the LORD was kindled against Moses, and he said, [Is] not Aaron the Levite thy brother? 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.