Marie,

I understand what you are saying.  Confronting the first co-worker could result in that person denying anything was said at all.

This is bullying and if someone said a comment like that to me, in work, I would take it further.  Likewise if I heard this said about someone I would not repeat it.  It's not professional to get involved in idle gossip like that.

I certainly would not confront anyone to hear more negative things said about me to my face.  

This needs nipped in the bud right away.