大乘起信論義記 3.106

3.106

前中二：先明真如內熏無明令成淨業，後即此淨用返熏真如增勢力。前即本熏，後即新熏。文處可見也。

In the former part there are two: first, it explains that tathatā internally perfumes avidyā, causing it to accomplish pure activity; second, that this very pure functioning in turn perfumes tathatā, increasing its power. The former is original perfuming; the latter is newly arisen perfuming. This can be seen from the text.