瑜伽論記 16.71

16.71

景云：問：三無色地，云何得有現行未知當知根耶？如下文說依四靜慮及初未至入於見道依九依定而盡諸漏？答曰：此據見道已前依色界定起煗等善根，因此則入無色定心趣求見道，如是展轉入三空皆起此行名未知當知根，非謂三空能入根本見道名有未知根。

Jing says: Question: In the three formless stages, how can there be the actively manifest faculty of that which has not yet been known and will be known? As a subsequent text states, one enters the path of seeing based on the four dhyānas and the initial unarrived [absorption], and exhausts all taints based on the nine foundational concentrations. The answer is: This is based on the stage prior to the path of seeing where, relying on concentrations of the form realm, one gives rise to the roots of good such as heat; by this means, one enters the concentration of the formless [realm] with a mind striving toward the path of seeing. Proceeding gradually in this way, one enters the three formless absorptions and in all of them gives rise to this practice; this is called the faculty of that which has not yet been known and will be known. It does not mean that the three formless absorptions can enter the root path of seeing and thus are said to possess the faculty of that which has not yet been known.