Exodus 4:6-8

ADONAI also said to him, “Now put your hand within your cloak.” So he put his hand inside, and when he took it out, his hand had tza'arat—white as snow. Then He said, “Put your hand back into your cloak.” So he put his hand back in, and when he took it out it was restored again as the rest of his skin. Then He said, “If they do not believe you, or listen to the voice of the first sign, they will believe the message of the latter sign.