If you're quoting only a small portion of a larger work, you really don't need their permission. Let's say you wanted to use a paragraph from one of my hubs to help explain something in yours. You can copy/paste that paragraph, use the quote feature to set it off from your other text, and then list my name and the title of my hub. Although I still retain the copyright for my work within your hub, you can use it by the "Fair Use" rule that is part of the copyright law.
That same rule applies to any other published work you want to quote. Here are things to remember:
1. It can only be a small portion of the entire work, unless you do get permission.
2. Always name your source - both the author's name and the title of the article, hub, book, etc.
3. The quote should be a very small part of a larger and unique work you've written.