俱舍論疏 13.187

13.187

論「勝義不善至猶如痼病」，答也。翻涅槃立生死，即生死名勝義不善。以生死中有漏之法皆是行苦、自性不安。性不安故，猶如痼疾，有此疾者，常不安穩。

The treatise says: "The ultimate unwholesome [...] is just like a chronic illness." This is an answer. By inverting nirvāṇa, saṃsāra is established; thus saṃsāra is called the ultimate unwholesome. Because contaminated dharmas within saṃsāra are all the suffering of conditioning and are inherently unpeaceful. Because their nature is unpeaceful, they are like a chronic illness; one who has this illness is constantly insecure.