Final answer:
The passage from 'The Canterbury Tales' indicating the knight's involvement in the Crusades is 'And he'd fought for our faith at Tramissene Three times in lists, and each time slain his foe.'
Step-by-step explanation:
The excerpt from the "General Prologue" of The Canterbury Tales that tells us the knight had been part of the Crusades is:
And he'd fought for our faith at Tramissene
Three times in lists, and each time slain his foe.
This passage indicates that the knight actively participated in battles that were part of the military expeditions aimed at winning the Holy Land for Christianity. The term “fought for our faith” clearly underscores the religious motivation behind the knight's participation in these conflicts, aligning with the historical context of the Crusades wherein Christian knights endeavored to reclaim Jerusalem and other sacred sites.