See also the instructions on the page In-text citations for secondary sources
In your research, you will often encounter resources where an author refers to another researcher's work or one author quotes from another's work. This source within a source is known as a 'secondary source' or 'indirect source'.
Referencing a source from a secondary source is generally discouraged since authors are expected to have examined the works they cite. However, it is not always possible to obtain the original publication - it may be published in another language, or in a book or journal which is out of print or difficult to obtain.
To cite a source from a secondary source, make it clear that you are citing a secondary sources in the text, and list only the secondary source in the reference list.
For example, Izumi Featherstone’s article refers to research undertaken in 1990 by Begley. If Begley’s work was also relevant to your own assignment you might decide that you also need to refer to Begley’s article in your writing. Where possible, you should try to obtain the original published work by Begley - in this case, a 1990 journal article - and read through the article to form your own opinions on his research. However, if it's impossible to access the original article, you may cite the secondary source.
The example above may be cited as below.
According to Begley's research as cited in Featherstone,1 ...
1. Featherstone IE. Physiological third stage of labour. Br J Mid. 1999;7: 216-21.