“Monks, even if bandits were to carve you up savagely, limb by limb, with a two-handled saw, he among you who let his heart get angered even at that would not be doing my bidding. Even then you should train yourselves: ‘Our minds will be unaffected and we will say no evil words. We will remain sympathetic, with a mind of good will, and with no inner hate. We will keep pervading these people with an awareness imbued with good will and, beginning with them, we will keep pervading the all-encompassing world with an awareness imbued with good will — abundant, expansive, immeasurable, free from hostility, free from ill will.’ That’s how you should train yourselves.
“Monks, if you attend constantly to this admonition on the simile of the saw, do you see any aspects of speech, slight or gross, that you could not endure?”
“Then attend constantly to this admonition on the simile of the saw. That will be for your long-term welfare & happiness.”
Kakacupama Sutta: The Simile of the Saw MN 21 translated by Thanissaro Bhikkhu