In the introduction to my thesis, I cite a lot of classical results from the 19th and early 20th century. Should I try and cite the original source for these results, or does that look like I am trying to bloat my list of references to look smart and I should rather find a good monograph/survey on the topic? If I do go with the second option though, does it suffice to mention the book at some point in the beginning and then say things like "Bernstein showed" pages later without further citing a reference for where or when Bernstein showed that? It feels wrong to have "Bernstein  showed" when  is not by Bernstein.
(One answer could be: I cite where I have it from. But those classical things I read mostly on Wikipedia or in lecture notes and then go and look for appropriate sources)