Whenever you can, take material from the original and not a secondhand source. But if you quote an author's quotation of a source you did not personally consult, put the abbreviation qtd. in (for quoted in) before the source you cite.
Quoted on your work
Samuel Johnson admitted that Edmund Burke was an "extraordinary man" (qtd. in Boswell 289).
Works Cited
Boswell, James. Boswell's Life of Johnson. Edited by Augustine Birrell, vol. 3, Times Book Club, 1912. HathiTrust Digital Library, hdl.handle.net/2027/uc1.b3123590.
