How do I cite a secondary (or indirect) source?
When an author writes about research done by another author, and you have not seen the original source which is referenced, that is called a secondary source (or indirect source, in MLA Citation Style). You can still use that information in your work, but how it should appear in your paper and in your bibliography will vary depending on the citation style you're using.
APA Citation Style
In APA Citation style, these are called secondary sources. Cite only the source you actually consulted, and use "as cited in" in your parenthetical reference to indicate you haven't seen the original source.
MLA Citation Style
In MLA Citation style, these are called indirect sources. Since you didn't read the original source, include only the source you did consult in your Works Cited list. The abbreviation “qtd. in” as part of your in-text citation indicates you haven't consulted the original source.
Chicago Citation Style
In Chicago Citation Style, these are referred to as citations taken from secondary sources. Both the original and the secondary source must be listed in the note and the bibliography.