Hilchos Lashon Hara chapter 7, section 4

The same is true if there is a rumor that someone did or said something that is not proper according to the Torah, whether it is a light sin or a serious one. It is forbidden to accept and believe it. One may only be cautious until the matter becomes clear.

And even more so, he must be very careful if he wants to tell others, not to intend to pass the rumor on and spread it further.