Because researchers are generally expected to have consulted the sources they cite, it is advised that you not cite a source quoted within another (secondary) source. You should rather consult the original source directly. If, however, you are unable to access the original source, the MLA Handbook recommends the following citation format:
IT: (qtd. in Bickerton 76)
WC: Bickerton, Derek. More than Nature Needs: Language, Mind, and Evolution. Cambridge: Harvard UP, 2014.
As shown in the above example, only the source you directly consult should be included in the parenthetical reference and the works cited list. The original source should be referenced in the text (immediately before the parenthetical reference) and may be cited more fully in a note. See the MLA Handbook (6.4.7, 6.5).
The format of the works cited entry depends, of course, on the kind of source you consulted. The above example cites a quote found in a book, so the entry follows the format for a book.