appropriate credit — If supplied, you must provide the name of the creator and attribution parties, a copyright notice, a license notice, a disclaimer notice, and a link to the material. CC licenses prior to Version 4.0 also require you to provide the title of the material if supplied, and may have other slight differences.

Maybe that could be just a link to the user page, but otherwise I would see it as needing to link to each message or comment they used.