瑜伽論記 3.192

3.192

又依一切生一切有生時而說者，一切四生一切三有受生之時定有識界，故偏說識，餘五不定，是故不說。

Regarding "Furthermore, it is stated according to all births and the time of birth in all existences": at the time of taking rebirth across all four modes of birth and all three realms of existence, the realm of consciousness is definitely present; therefore consciousness is singled out, while the other five are not definite, and are therefore not stated.