SORROWFUL ARE ALL CONDITIONED THINGS
Sabbe sankhara dukkha'ti yada pannaya passati
Atha nibbindati dukkhe esa maggo visuddhiya.
All conditioned things are sorrowful. When one sees this in wisdom, then he becomes dispassionate towards the painful. This is the Path to Purity. 
The story is the same as the story onanicca. Here the Buddha on reflection found that another group ofbhikkhushad meditated ondukkha. So, he said, 'Bhikkhus, all component things are oppressive and unsatisfactory, thus all component things aredukkha