Answered By: Sara Marks Last Updated: Jan 14, 2020 Views: 3
This is called "Cited within" by most styles. Your best bet is to get the article or book they cited originally and just use that.
If you can't get that source (and that will happen, especially if you're using original and historical sources), then you want to figure out the way the style you're using wants you to cite within. The links give you the most common styles.