大般涅槃經疏 14.17

14.17

第六觀冤憎會苦。既從合會緣生，生即是苦前境偪心，心領境偪憂惱，故名冤憎會苦。

Sixth, contemplating the suffering of association with what is hated: since it arises from the conditions of coming together, this arising is itself suffering; the object in front oppresses the mind, and the mind registers the oppression of the object with grief and distress, therefore it is called the suffering of association with what is hated.