Ask the Library: Reference

This is called an indirect citation.

From the MLA handbook:

6.4.7 Citing Indirect Sources

Whenever you can, take material from the original source, not a secondhand one.  Sometimes, however, only an indirect source is available -- for example, someone's published acount fo another's spoken remarks.  If what you quote or paraphraes is itself a quotation, put the abbreviation qtd. in ("quoted in") before the indirect source you cite in your parenthetical reference.

Example:

Samuel Johnson admitted the Edmund Burke was an "Extraordinary man" (qtd. in Boswell 2: 450)

Work Cited

Boswell, James. The Life of Johnson. Ed. George Birbeck Hill and L. F. Powell. 6 vols. Oxford:Clarendon, 1934-50. Print