Q. How can you cite a source that you found in another source using APA style?

A good written paper reflects your own analysis and interpretations of sources you have read instead of collation of claims, analysis and interpretations of the work done by others. In situation where it was not possible, for example, the stated work is out of print, or unavailable through your usual sources, you may cite as follows :-

If you read an article written by Walsh and Downe, in which they cited a claim from a previous study by Silverman, and you wish to refer to this information in your assignment:

• You would acknowledge Silverman in your paper like :
  As per Silverman’s claim (as cited in Walsh & Downe, 2005) ……
  This is an important claim ..... (Silverman, 1984, as cited in Walsh & Downe, 2005)
  Silverman claimed “qualitative researchers risk further marginalization from policymakers and clinicians if their work remains isolationist and esoteric, and seemingly incapable of influencing either strategy or practice” (as quoted in Walsh & Downe, 2005, p. 110) and found that .....
  Because the above passage contains a quote, the in-text citation requires not only the name and date of publication of the source, but also the page number.
   
• In your Reference list at the end of your assignment, your entry would be a reference for Walsh and Downe's article because that is where you sourced the information:
  Walsh, D., & Downe, S. (2005). Meta-synthesis method for qualitative research: a literature review. Journal of Advanced Nursing, 50(2), 204-211. doi:10.1111/j.1365-2648.2005.03380.x