How Do I Recover the Clone Stamp Source Panel?

I accidentally closed the clone stamp source panel, and I can't figure out how to open it back up. I need to adjust the size of the clone stamp (the W and H %), and I'm not sure of any other way to do this. I've tried reseting the tool, and that didn't work.

If anyone has any experience with this and could help me out, it would be appreciated very much! Thanks in advance.