My source quotes another source. 

In the text, cite the original source.  Make the works cited entry like below:   

Jones, Michael.  "Today's Blog".  Michael's Blogs. 
XXX8 January 2006.  www.mikeblog.com  as quoted by
XXX Jim Roberts.  Idiots on the Internet.  Accessed 9
XXX Sept 2010.  www.myopinionsrock.com