八識規矩補註 2.15

2.15

謂第六識呼此第七為染淨依也。蓋由此識有漏、內常執我故，令第六識念念而成於染；由此識無漏、恒思無我故，令第六識念念而成於淨。是以第六成染成淨，皆由第七也。

This means that the sixth consciousness designates this seventh [consciousness] as the basis of defilement and purity. For, because this consciousness is contaminated and constantly grasps a self internally, it causes the sixth consciousness to become defiled from moment to moment; because this consciousness becomes uncontaminated and constantly contemplates selflessness, it causes the sixth consciousness to become pure from moment to moment. Thus, whether the sixth becomes defiled or becomes pure is entirely due to the seventh.