An "academically correct" solution (i.e., not to taint the prestige of a scholar who cites the solution) would be to cite a real, proxy scholar who checks the solution, but gives all credit to the anonymous 4chan user. Scientists often abhor citing from blogs, forums, and Wikipedia, as those publications "are not peer-reviewed by trustworthy professionals".
For wikipedia, you should reference the specific version of the article, which will never change.
For blogs, or wikipedia articles you feel might get deleted, you can reference a specific version from archive.org.