A man wished to serve a lavish meal to a famous teacher as a means of honoring him. He sought permission from the teacher the night before, and the following day, served him the lavish meal.
Some time later, the man was murdered. When news of the murder reached the teacher, the teacher said, “Whatever enemies might do to enemies, the ill-directed mind can do to you even worse.”
Adapted from the sutra at this link: http://www.accesstoinsight.org/tipitaka/kn/ud/ud.4.03.than.html