Not trying to be a jerk, but how do you know this to be true?

I don't know it to be true. Again, would or even could the FBI go to a judge with a single sworn affidavit of information merely claiming that one person had seen classified documents at Mar-a-Lago??? The FBI could not possibly consider getting a search warrant on a popular ex-president relying on a single claim of wrongdoing. They had been working on how to orchestrate this raid for two weeks before it happened. It wasn't spontaneous, but the culmination of careful planning. Elsewhere, supposedly reliable rumors claim that a tapped phone call figured into the warrant application.

@racocn8 Thank you, I wasn’t aware of a tapped phone call.