You shall not spread a false report. You shall not join hands with a wicked man to be a malicious witness.
#exodus 23:1 #mishpatim

Did you think Paul was making a new command when he said not to engage in vain and worthless talk? Think again. As with everything else he wrote, he was teaching Torah. If talking about someone else serves no useful or edifying purpose, then don't do it. It doesn't matter if it's true. Keep it to yourself.