瑜伽論記 7.320

7.320

若等分行人，隨所愛樂攀緣彼境，勤修加行。如是勤修，唯令心住，非淨其行者，等分行人所起煩惱盡不偏增，不可別觀不淨等境，但隨所樂或觀無常苦空等唯令心住，非如偏增別淨其行，故云非淨其行。

Regarding "If a practitioner of equal proportions, taking whatever focal object they delight in as their object, diligently cultivates preparation; cultivating diligently in this way merely causes the mind to abide, not purifying their practice": the afflictions arising in a practitioner of equal proportions are entirely without predominance, so they cannot specifically contemplate objects such as impurity, but merely, in accordance with whatever they delight in, contemplate impermanence, suffering, emptiness, and so forth merely to cause the mind to abide; it is not like those with a predominance who specifically purify their practice. Therefore it says "not purifying their practice".