What is the source of the allusion in the sentence below?
As we hiked through the snow-covered woods, we remembered the weather forecaster's predictions, which seemed in retrospect rather Panglossian.

 - the Bible
 - literature
The source of the allusion Panglossian is literature.
In Voltaire's 1759 novel Candide, Pangloss is a tutor whose worldview is relentlessly upbeat to the point of excessive optimism.
The allusion Panglossian means unreasonably positive.