It is always best to cite information from the original source. Sometimes, however, the only available source may be an indirect one. Within the text of your paper, cite the item used, not the item quoted, and within the parenthetical reference, the name and page number are preceded by the abbreviation, “qtd. in”. (See p. 226, MLA Handbook, 2009)
Samuel Johnson admitted that Edmund Burke was an “extraordinary man” (qtd. in Boswell 450).
For your list of works cited, give the indirect source (