成唯識論演祕 4.707

4.707

釋曰：應謂彼言，此不應記。不解彼問，名為默記，非總亡言，名默記也。

The Explanation states: One should say to them, 'This should not be answered.' Leaving their question unexplained is called answering in silence; it is not that a complete absence of speech is called answering in silence.