According to the Constitution, one can only be convicted of treason if 2 or more witnesses testify to the act.
Count me in ... are you willing to testify as well?
Hearsay testimony won’t pass Constitutional muster.
I can't claim to have heard the words from his own mouth, even though I have no reason to doubt that this report that he uttered them is accurate.
Your challenge is an interesting one nonetheless...
"Would I?" if I could truthfully do so, and was in the position of being needed for that task...
Yes.