Trung Bộ Kinh (Majjhima Nikaya) 3:100
SUJATO‘virāgānupassī assasissāmī’ti sikkhati, ‘virāgānupassī passasissāmī’ti sikkhati;
or observing fading away,
‘virāgānupassī assasissāmī’ti sikkhati, ‘virāgānupassī passasissāmī’ti sikkhati;
or observing fading away,