Hilchos Rechilus, chapter 9, section 2
They are as follows:
a) One must be very careful to not immediately decide that harm will result but first carefully
consider the matter.
b) One must not exaggerate the evil involved.
c) One’s intent must be only for beneficial purpose, to remove harm from Shimon and not
because one hates Reuven.
(This rule includes something else. One must consider whether the beneficial result will come
about, for often Shimon will not listen and join the partnership anyway. Then, when Reuven
annoys him later he will say to him: So and so was right correct he warned me from joining you,
and suchlike. One may not inform someone like this whom one knows speak rechilus regularly,
for through this one will cause him to transgress the Torah prohibition of rechilus.)
d) If one can prevent the partnership without speaking rechilus one should not speak about
Reuven to Shimon.
e) The leniency only applies if Shimon will leave the partnership and not harm Reuven in
any other way. If Reuven will suffer other harm through one’s story, more conditions must be
fulfilled as explained later in paragraphs 5 and six. This applies even more if one sees that one’s
story will cause Reuven more harm than he deserves according to law. See later paragraph 9
what we write about this.