First, you should find the original source of the quotation, did it come from a book, article, speech, poem, essay? Ideally, you would want to use the citation from the original work. For example, "I don't understand it, and I don't like what I don't understand." This is from the book Charlotte's Web. It is a known by some people, but it isn't really famous and therefore would not be considered common knowledge. So this quote would need to be cited. You would cite the author, year, and page number in your paper as an in-text citation and then do a regular book citation for your References page.
Sometimes, quotes are so often used that they are considered "common knowledge." For example, "Nothing to fear, but fear itself." This phrase comes from the 1933 inaugural address of Franklin D. Roosevelt. Many people know this quote, even if they cannot remember who said it. This would qualify as "common knowledge". Things that are common knowledge do not have to be referenced on your Reference page. For more information on what is or is not considered common knowledge, see the article from Prudue's OWL Is it plagiarism yet?
If you can't find the original citation information, then cite the document where you read the quote. For example, if you found a quote from Ralph Waldo Emerson in a book of famous quotes, you would cite the book of famous quotes.
Remember that citations give the reader enough information to find your sources.
For additional help with citations and writing style, see the AU Academic Support Center guide to citations or make an appointment with a writing tutor.
