Quotes are text passages that are taken over verbatim. Do they therefore pose a risk through duplicate content?
Using quoted text passages from other websites on your own website does not constitute a duplicate content problem. You also will not get hit by a Google Penalty because of it, provided you properly cite the source for the text in the source code. In this article, you will learn how this works and what Google has to say about it.
Correctly citing quotes in the source code
Quotations or quoted text passages are not identified as duplicate content. However, you should ensure that the quotes are properly cited within the source code, as follows:
<blockquote>Here is the quoted text <cite>Here is the name of the quoted author or the source</cite></blockquote>
When citing content, it is therefore imperative to pay attention that the semantic markup in the source code is correct.
What Google says
Let's take a couple examples. One is you're a regular blogger, and you just want to quote an excerpt, some author you like or some other blogger who has a good insight. Just put that in a block quote, include a link to the original source, and you're in pretty good shape. If that's the sort of thing that you're doing, I would never worry about getting dinged for duplicate content. We do have good ways of detecting that sort of thing without any sort of issue at all.
Source: Matt Cutts