大乘義章 8.74

8.74

次就內外分別諸界。於中若就三分論之，六根是內、六塵是外、六識為中。兩分論之，根塵如上，六識不定。毘曇法中，攝之為內，故彼論言「內界說十二」。《成實》不爾，彼宗六識法入所攝，是則六識攝之在外（此三門竟）。

Next is distinguishing the elements in terms of internal and external. Therein, if discussed in terms of a threefold division: the six faculties are internal, the six dust-objects are external, and the six consciousnesses are intermediate. If discussed in terms of a twofold division: faculties and dust-objects are as above, while the six consciousnesses are unfixed. In the Abhidharma system, they are subsumed under the internal; hence that treatise states, 'Twelve are stated to be internal elements.' The Tattvasiddhi is not like this: in that school, the six consciousnesses are subsumed under the phenomenon-sense-base; therefore, the six consciousnesses are subsumed under the external. (This concludes the third section.)