Someone posted a response to a question on a Q&A website known was Quora (you may have heard of it). The credentials on his profile indicate that he possibly may be a credible person. However, I still wish to confirm, so what is the best way I can ask where the person got his information from without sounding as if the respondent doesn't know much about the topic?
I tried variations of those multiple times, never got an answer that indicates that I wasn't polite or that I was rude.
Thanks/nice/cool! How you succeeded in finding this information? I was also looking for it and couldn't find any source on the internet.
It's interesting, I wonder "bla bla bla" could you share your source so that I can read further about this topic?
I'd like to use the information in this answer in another place, but I need to supply a source for that. Could you share it with?
I heard people doubtful about it - could you attach your sources so it will be more reliable for them?
It sounds you really know this topic! How you discovered it / Where you found that information?
In general, the approach I'm taking is to try not to sound critical; compliment about the answer quality, information, knowledge; and ask for the source for myself or for others that might be interested in it. Personally I think that a source improves the completeness of the answer, and it's best for everyone to have access to it (think about a situation where someone finds this answer a few years later and have another question or thought).
Another point is, that it depends on what's common on that site.
Is it a rule or guidance of the site to support your answer by sources? Did the person who asked the question requested sources?
If so, you have a "stronger case" for asking for sources, and I think you could ask it more directly (you can state that it's to improve the answer according to the site's customs).