妙法蓮華經玄義 1.230

1.230

而復言神通延壽，是何神通？若作意神通，同彼外道；若無漏神通，同彼小乘；若實相神通，則非延、非不延，能延、能不延。能延，何止延壽，而不延眼令見佛性？何不延舌說於常住？眼不見性，則知非實相神通，非麁何謂？前一難已知麁，後難重來耳。

Furthermore, you say that supernatural powers extend the lifespan—what kind of supernatural powers are these? If they are intentional supernatural powers, they are identical to those of non-Buddhists; if they are outflow-free supernatural powers, they are identical to those of the Hīnayāna; if they are real-mark supernatural powers, they neither extend nor do not extend, yet can extend and can refrain from extending. If they can extend, why stop at extending lifespan and not extend the eyes to cause them to see the Buddha-nature? Why not extend the tongue to speak of eternal abiding? When the eyes do not see the nature, one knows they are not real-mark supernatural powers; if not coarse, what are they called? From the former challenge [coarseness] is already known; the latter challenges are merely repeated.