成唯識論了義燈 2.25

2.25

一微量唯二微果上者，以彼父母二微合，生子微之上，有此微量。以為根取最細之色，不與父母合者，以非根境故。

'The atomic dimension (aṇu-parimāṇa) resides only on the effect of two atoms (dvyaṇuka)': because when the two parent atoms combine, they produce a child atom, and upon this [child atom] there is this atomic dimension. It is taken to be the subtlest form apprehended by the sense faculty, and it does not combine with the parent atoms, because they are not the objects of the sense faculties.