大乘起信論別記 1.111

1.111

言「不覺而起」者，心體為此無明所熏，動作生滅故名起。又即此心體由無明熏，轉成能見，乃至轉成起念相續。如是心體，有此五用，對境界能生意識，故名為意。此中第五，猶是意識，而約生後義，通入意中攝。

As for "arising due to non-enlightenment": the mind-essence, perfumed by this avidyā, moves to produce arising and ceasing, hence it is called "arising." Furthermore, this very mind-essence, through the perfuming of avidyā, turns into the perceiver, and further turns into the continuity of producing thoughts. Such a mind-essence has these five functions, and when facing external objects it is able to produce the manovijñāna; therefore it is named manas. Herein, the fifth is still manovijñāna, but in terms of the meaning of producing what follows, it is comprehensively subsumed under manas.