Exodus 4:6-8

Then the LORD said to Moses, “Put your hand inside your coat.” So Moses put his hand inside his coat. When he took it out, it was white with a skin disease. Then he said, “Now put your hand inside your coat again.” So Moses put his hand inside his coat again. When he took it out, his hand was healthy again, like the rest of his skin. Then the LORD said, “If the people do not believe you or pay attention to the first miracle, they may believe you when you show them this second miracle.