I've been looking for a reference for the story of the conflict between Kosalan king Vidubhara and the Sakyans, that the Buddha tried to stop. There are several versions of this on the web, but none of them give any references. Is it canonical? Whether it's canonical or not, where does it come from?
Late Upasaka Goenka gave a very detailed teaching, based on cannonical references: Why Was the Sakyan Republic Destroyed?, Robert Michael.
On seeing the importance here: Dhamma is unwisely grasped, if used for politic and wordily gains:
One should not make an effort everywhere, should not be another's hireling, should not live dependent on another, should not go about as a trader in the Dhamma.
[Note: This is a gift of Dhamma and not meant for commercial purpose or other low wordily gains by means of trade and exchange.]