Digha Nikaya 2:329
SUJATOSamudayadhammānupassī vā dhammesu viharati, vayadhammānupassī vā dhammesu viharati, samudayavayadhammānupassī vā dhammesu viharati.
They meditate observing the principles as liable to originate, as liable to fall, and as liable to both originate and vanish.