I'm seeking the source of the following quotation:
"In prison, there were no rifles for training, no stone fortresses from which to shoot. Behind those walls, our rifles were books. And through study, stone by stone we built our fortress, the only one that is invincible: the fortress of ideas."
I would like to find the primary source (speech, autobiography, newspaper article, interview, whatever it may be). If I can't find the primary source, any authoritative reference such as a reputable collection of quotations will do. I need the full citation, including page number, publisher, year, etc.
This has been particularly frustrating, because almost all references to this quote are on anti-Castro websites, none of which cite the source of the quote.
I may have more requests for help with quote verification in the coming weeks. Thank you.