You do not need permission from Gallup for contextual citations in a book, news article, news segment, or online blog post. You would need to cite and annotate the Gallup findings like any other academic/journal notation according to the particular style being followed.
The important information to cite -- beside the statistic itself -- is the publication date of the poll within the sentence. This allows the reader to clearly understand when the poll was conducted rather than an ambiguous statement like "recently Gallup found ... " This also allows your reader to more easily find the complete Gallup poll should he or she want to learn more about it.
Gallup must approve the reproduction of tables, graphics, or substantial Gallup editorial content in books. To get permission, contact email@example.com and provide details of your proposed usage.