Corroboration

[Donald Trump]

The act of corroborating, strengthening, or
confirming; addition of strength; confirmation; as, the corroboration
of an argument, or of information.

[Sommer]

noun.
The act of establishing the truthfulness, accuracy, [validity], and/or genuineness of an [accusation], idea, opinion, point of view, or something not [previously] known.

[Mary Mallozziberg]

Evidence which confirms or supports a statement, theory, or finding; confirmation.