成唯識論述記 5.194

5.194

述曰：第七末那以思量為自性故，《對法》第二、《攝論》第一、六十三皆云思量是意，即自證分。前第八識了別是行相，今既言意，故意即是第七行相，即是見分，體性難知，以行相顯。其實思量但是行相，其體即是識蘊攝故。

The Commentary states: Because the seventh, manas, has cogitation as its essential nature, the second fascicle of the Abhidharmasamuccaya, the first fascicle of the Mahāyānasaṃgraha, and the sixty-third fascicle [of the Yogācārabhūmi] all say that cogitation is manas, which is the svasaṃvittibhāga. Earlier, for the eighth consciousness, discernment was the ākāra; now, since it is called 'manas', manas is therefore the ākāra of the seventh consciousness, which is the darśanabhāga. Its essential nature is difficult to know, so it is revealed through its ākāra. In reality, cogitation is merely the ākāra, and its substance is subsumed under the aggregate of consciousness.