Destruction of Books in Jihad

A quote attributed to Kitab al-Wagiz fi fiqh madhab al-imam al-Safi'i states that during Jihad: > One must destroy their useless books. However, when I searched online, most results were from anti-Islamic blogs and forums that merely repeat the quote without offering any context. I would like to read the original quote in its full context. Additionally, I want to understand its proper meaning as understood by devout Muslims. Does it mean that all books are to be destroyed, or is there a specific criterion that makes a book "useless"?