俱舍論記 3.105

3.105

「無苦根者至惱害事故」者，釋色界無憂、苦。身淨妙，故非苦依。無不善法，故無苦境。由奢摩他潤相續身，故非憂依。無惱害事，故無憂境。

Regarding "Lacking the faculty of pain ... harmful circumstances": this explains why the form realm lacks grief and pain. Because the body is pure and exquisite, it is not a basis for pain. Because there are no unwholesome phenomena, there are no cognitive objects of pain. Because the continuous physical body is moistened by calm abiding (*śamatha*), it is not a basis for grief. Because there are no harmful circumstances, there are no cognitive objects of grief.