"Firsthand evidence" refers to information or knowledge that someone has personally experienced or observed themselves. It is direct proof or testimony that comes from direct experience, rather than secondhand information or hearsay. Full definition
She has seen firsthand the evidence that it results in solid learning. (educationworld.com)
Similarly, if the conduct of counsel is the subject matter of a proceeding, such as a motion for costs under rule 57.07 or more a motion brought to compel undertakings under rule 34.15, then, once again, counsel will likely be best suited to provide firsthand evidence of relevant facts. (slaw.ca)
A new study examining the muscular system of bonobos provides firsthand evidence that the rare great ape species may be more closely linked to human ancestors than common chimpanzees. (sciencedaily.com)