俱舍論疏 3.138

3.138

論「無憂根者至惱害事故」，釋無憂所以也。一以所依身定潤故無憂，二以無憂境故無憂也。

The commentary states: "Those lacking the faculty of grief [...] things that afflict and harm." This explains the reason for lacking grief: first, because the basis, the body, is moistened by meditative concentration, they lack grief; second, because there are no sorrowful objects, they lack grief.