俱舍論頌疏論本 3.32

3.32

及三定心悅者，心謂第六意識。此第三定，心相應受能攝益者，亦名樂根。謂第三禪，五識無故，無身受樂，唯心悅名樂也。

"As is mental pleasure in the third dhyāna" means: "mind" refers to the sixth, the mental consciousness. In this third dhyāna, feeling associated with the mind that can comfort and benefit is also called the pleasure faculty. That is to say, in the third dhyāna, because the five sense-consciousnesses are absent, there is no physical feeling of pleasure; solely mental pleasure is called pleasure (sukha).