妙法蓮華經玄義 6.96

6.96

無問自說有二種：一、理深意遠，人無能問。二、非不可問，但聽者宜聞，佛為不請之師，不請之師不待問自說也。

Unprompted speech (udāna) is of two kinds: 1. The principle is deep and the meaning is profound, so no one can ask. 2. It is not that it cannot be asked, but that the listeners ought to hear it; the Buddha acts as an unasked teacher, and an unasked teacher preaches of himself without waiting for questions.