八識規矩補註 2.27

2.27

謂此第八極微細故，所以二乘愚法聲聞不信有此第八識，唯以前六識等受熏持種。為彼智淺心麁而迷執者也。

Because this eighth [consciousness] is extremely subtle, the śrāvakas of the two vehicles who are foolish regarding dharmas do not believe that this eighth consciousness exists, and take only the first six consciousnesses and so forth to receive perfuming and sustain seeds. This is because their wisdom is shallow, their minds are coarse, and they are confused and attached.