Маджхима Никая 2:108
SUJATOsamudayadhammānupassī vā cittasmiṁ viharati, vayadhammānupassī vā cittasmiṁ viharati, samudayavayadhammānupassī vā cittasmiṁ viharati.
They meditate observing the mind as liable to originate, as liable to fall, and as liable to both originate and vanish.