Then Moses answered, “But behold, they will not believe me or listen to my voice, for they will say, ‘The LORD did not appear to you.'” The LORD said to him, “What is that in your hand?” He said, “A rod.” And he said, “Cast it on the ground.” So he cast it on the ground, and it became a serpent; and Moses fled from it. But the LORD said to Moses, “Put out your hand, and take it by the tail” –so he put out his hand and caught it, and it became a rod in his hand– “that they may believe that the LORD, the God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, has appeared to you.” Again, the LORD said to him, “Put your hand into your bosom.” And he put his hand into his bosom; and when he took it out, behold, his hand was leprous, as white as snow. Then God said, “Put your hand back into your bosom.” So he put his hand back into his bosom; and when he took it out, behold, it was restored like the rest of his flesh. “If they will not believe you,” God said, “or heed the first sign, they may believe the latter sign. If they will not believe even these two signs or heed your voice, you shall take some water from the Nile and pour it upon the dry ground; and the water which you shall take from the Nile will become blood upon the dry ground.” But Moses said to the LORD, “Oh, my Lord, I am not eloquent, either heretofore or since thou hast spoken to thy servant; but I am slow of speech and of tongue.” Then the LORD said to him, “Who has made man’s mouth? Who makes him dumb, or deaf, or seeing, or blind? Is it not I, the LORD? Now therefore go, and I will be with your mouth and teach you what you shall speak.”
–Exodus 4:1-12