Maybe you are running a sangha and need to know where the line is to ban a member.
The Buddha gave this advice in a Sutta called Trash.
The short reason is: some bad barley spoils the bunch.
At one time the Buddha was staying near Campā on the banks of the Gaggarā Lotus Pond. Now at that time the mendicants accused a mendicant of an offense. The accused mendicant dodged the issue, distracted the discussion with irrelevant points, and displayed annoyance, hate, and bitterness.
Then the Buddha said to the mendicants, “Mendicants, throw this person out! Throw this person out! This person should be shown the door. Why should you be vexed by an outsider?
Take a case where a certain person looks just the same as other good-natured mendicants when going out and coming back, when looking ahead and aside, when bending and extending the limbs, and when bearing the outer robe, bowl and robes. That is, so long as the mendicants don’t notice his offense. But when the mendicants notice the offense, they know that he’s a corrupt ascetic, just useless trash. When they realize this they send him away. Why is that? So that he doesn’t corrupt good-natured mendicants.
Suppose in a growing field of barley some bad barley appeared, just useless trash. Its roots, stem, and leaves would look just the same as the healthy barley. That is, so long as the head doesn’t appear. But when the head appears, they know that it’s bad barley, just useless trash. When they realize this they pull it up by the roots and throw it outside the field. Why is that? So that it doesn’t spoil the good barley.
In the same way, take a case where a certain person looks just the same as other good-natured mendicants when going out and coming back, when looking ahead and aside, when bending and extending the limbs, and when bearing the outer robe, bowl and robes. That is, so long as the mendicants don’t notice his offense. But when the mendicants notice the offense, they know that he’s a corrupt ascetic, just useless trash. When they realize this they send him away. Why is that? So that he doesn’t corrupt good-natured mendicants.
This goes on for some ways.
I originally read it in this book
The Buddha’s Teachings on Social and Communal Harmony - Edited and introduced by Bhikkhu Bodhi
v1.0 - Last edit 8-July-2024
This is work dedicated to the Public Domain via CC0 1.0