Sometimes, a textbook will quote an excerpt of another book or novel that you would like to reference in your paper. MLA style outlines specific guidelines for citing a source within a source, but, when possible, it is better to locate and cite the original source.
Citing an Excerpt
Let's say your history textbook includes a poem that you would like to quote in your paper. If you don't have the time or means to find the original source, you should include the textbook in which you found the excerpt on your "Works Cited" page. In the internal citation for that particular quote, you should indicate that the information was quoted within the source you are citing by writing "qtd. in" before the usual citation.
Here is an example of how you would do this in a paper:
As Langston Hughes asks in his poem, "What happens to a dream deferred?" (qtd. in Smith 244).
Citing the Original Source
The most accepted way of citing a source within a source by locating the original quote or excerpt, which might require a trip to the library some savvy Internet searching. Once you find the original source, you can use this information your Works Cited page and for your internal citations.