Yeah, but it's not your original content and you didn't give any attribution to the original author who holds the copyrights and all other rights on its written content.

In other words, it doesn't have to be a problem to use such citation the way you did, but same as you wouldn't like that somebody else just come and copies a portion of your text and pastes it elsewhere (without providing the source link to your original writings) and even earn some money with it, the same way might feel the author of the introductory chapter that you used in your article without giving the source link and attributing the author.