俱舍論疏 8.107

8.107

論「初靜慮中至故言想一」，此釋諸地想不同也。初靜慮中言想一者，是戒禁取，故言染污。第二靜慮是定心故，名為善想。第三定中受異熟樂無厭捨故，名為想一，無記相也。

The verse commentary states: "In the first dhyāna [...] is therefore said to be 'one perception'." This explains the differences in perception across the various stages (bhūmi). In the first dhyāna, what is termed "one perception" is the adherence to rules and rituals (śīlavrataparāmarśa); hence it is called defiled. Because the second dhyāna is a concentrated mind, it is called wholesome perception. In the third dhyāna, because one does not feel aversion to or renounce the pleasant feeling of vipāka, it is called "one perception," which has an indeterminate (avyākṛta) characteristic.