Question:
Are you allowed to listen to loshon hora about a Jew from a non-Jew?
Answer:
One should not listen, because as a result of what he heard from the non Jew he will now look down upon the Jew disgracefully.
Sources:
Chofetz Chaim, Hilchos Rechilos, Mekor Chaim Klal 6:3 & footnotes there.