Document, Document, Document!!!
Documenting what was said, even with witnesses present, contemporaneously with the event, is the most reliable method to preserve evidence and a good business practice.
Almost all employment disputes arise when the relationship goes sour so what does not seem important at the time may be the source of a multimillion dollar lawsuit instituted years later.
No matter how busy you are, the few minutes it takes to document an event could be the exhibit that a jury will rely upon in exonerating you and your employer!