How do you cite a source that you found in another source?

Use secondary sources sparingly, for instance, when the original work is out of print, unavailable through usual sources, or not available in English. Give the secondary source in the reference list; in text, name the original work and give a citation for the secondary source.

For example, if Allport's work is cited in Nicholson and you did not read Allport's work, list the Nicholson reference in the reference list. In the text, use the following citation:

Allport's diary (as cited in Nicholson, 2003).

(adapted from the sixth edition of the APA Publication Manual, © 2010)