It's not enough to have heard something. If you want to allege something as fact, you have a duty to investigate the accuracy of the alleged facts. If someone tells me you raped little girls, I have an obligation to investigate that claim before broadcasting it on national TV. I don't have to prove it as fact, but I have to do enough investigation to be non-negligent in repeating that claim, which means finding evidence for that claim, and to have considered evidence contradicting it. My position that you did rape little girls has to be a reasonable one, based on the facts available to me, and I can't not search for those facts and claim ignorance as a defense.
If I made that claim today, and it ruined your business, you'd correctly (I assume...) sue me for defamation, and win, because there are no facts or evidence supporting my allegation, even if someone on Twitter said you did.