When quoting someone else's quotes for historical references, you say
- Quoted in REFERENCE, page [xxx.]
Anthony Robbins was successfully sued over the use of a couple of TWO-WORD phrases. There is no word count limit that determines fair use, and if you're getting paid to write the book, it's a "commercial purpose."
There's an excellent article about this on Ivan Hoffman's website at, http://www.ivanhoffman.com/fair3.html. Ivan's entire site http://www.ivanhoffman.com/ has many, many useful articles. He is an attorney who specializes in copyright and intellectual property law. There are two previous articles on other aspects of fair use, as well.
Keep in mind that Hoffman's articles are not intended as legal advice and are not legal advice. The articles are intended to provide only general, non-specific legal information and are not intended to cover all the issues related to the topic discussed.
Chapter 5 - Copyrights, Previously Published Works,and Using Quotations: http://tinyurl.com/38t4xpd
Next: Chapter 6 - Permissions and Writer Beware: http://tinyurl.com/3a9yfby