The Buddha once explained to the monks that there are five aspects of speech by which others may speak to them: “timely or untimely, true or false, affectionate or harsh, beneficial or unbeneficial, with a mind of good-will or with inner hate.” [i] In these circumstances, they should train themselves by thinking: “Our minds will be unaffected and we will say no evil words. We will remain sympathetic to that person's welfare, with a mind of good will and with no inner hate. We will keep pervading him with an awareness imbued with good will and, beginning with him, 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.” [ii]
The Buddha continued that even if robbers were to carve the monks up limb by limb, with a two-handled saw, the monk who became angry even at that would not be doing the Buddha’s bidding. He instructed the monastics that even under such circumstances, they needed to train themselves to maintain an unaffected mind and to continuously pervade the universe with thoughts of goodwill, by eliminating hatred and not speaking evil words.
The Buddha asked if there would be any speech they could not endure were they to follow this guidance. They responded that there was none. He then told them that they should call to mind often the Simile of the Saw, for doing so would bring them happiness and great benefit.
[i] Thanissaro Bhikkhu, Kalama Sutta, AN III.65 (1994) (http://accesstoinsight.org/canon/sutta/anguttara/an03-065.html)
[ii] Ibid.