成唯識論了義燈 6.167

6.167

准《瑜伽》十二，云何空三摩地？空有四種，一觀察空，謂觀察諸法空無常、樂，乃至空無我及我所等。此有二解，一云，苦下四行俱是空行。無彼常、樂、我及我所，皆名為空；一云，但言無常無樂，不言是苦，但空、無我是空等持。

In accordance with the Yogācāra, fascicle twelve: "What is the emptiness samādhi? Emptiness has four types: first, observing emptiness, which refers to observing phenomena as empty of permanence and pleasure, up to empty of self and mine, and so forth." On this there are two explanations. One says: the four practices under suffering are all practices of emptiness; lacking that permanence, pleasure, self, and mine are all called empty. One says: it only says impermanent and devoid of pleasure, without saying suffering; only emptiness and non-self constitute the samādhi of emptiness.