"I am the only witness of Tradition" - Bl. Pius IX
What is the context of your quote? On the surface it is meaningless, since all true Catholics are witnesses to Tradition.
I must apologize for misquoting Bl. Pius IX. The substance of the quote is the same, but I must have confused it with the apocryphal "I am tradition!" quote.
The Pope, it is said, upbraided him, a bishop of the Pontifical States and a cardinal, for opposing him. Guidi was surprised, and said he had maintained only that bishops are witnesses of tradition. 'Witnesses of tradition?' said Pius; 'there's only one; that's me.'55 ... the above is cited from Dupanloup's private journal ... In saying this, if he did say it, Pius spoke as 'private theologian'! (Dom Cuthbert Butler, The Vatican Council 1869-1870, p. 355)