大乘起信論義記 3.91

3.91

熏習義者，如世間衣服實無於香，若人以香而熏習故則有香氣。此亦如是，真如淨法實無於染，但以無明而熏習故則有染相。無明染法實無淨業，但以真如而熏習故則有淨用。

The meaning of perfuming is: just as worldly clothes actually have no fragrance, yet if a person perfumes them with incense, then there is fragrance. This is also like that: the pure phenomenon of tathatā actually has no defilement, but only because avidyā perfumes it, there are marks of defilement. The defiled phenomenon of avidyā actually has no pure action, but only because tathatā perfumes it, there is pure function.