Exodus 4:6-8

6 Again, the Lord said to him, "Put your hand inside your cloak." He put his hand into his cloak; and when he took it out, his hand was leprous, as white as snow.
7 Then God said, "Put your hand back into your cloak"—so he put his hand back into his cloak, and when he took it out, it was restored like the rest of his body—
8 "If they will not believe you or heed the first sign, they may believe the second sign.