1-12.
The Set of Twelve Discourses Beginning with the Ganges River
417-428.
"Just as, monks, the river Ganges slants towards the east, slopes towards the east, inclines towards the east;
so too, monks, a monk developing the four establishments of mindfulness, cultivating the four establishments of mindfulness, slants towards Nibbāna, slopes towards Nibbāna, inclines towards Nibbāna.
"And how, monks, does a monk developing the four establishments of mindfulness, cultivating the four establishments of mindfulness, slant towards Nibbāna, slope towards Nibbāna, incline towards Nibbāna? Here, monks, a monk dwells observing the body in the body, ardent, fully aware, mindful, having removed covetousness and displeasure regarding the world; in feelings... etc. In mind... etc. He dwells observing mental phenomena in mental phenomena, ardent, fully aware, mindful, having removed covetousness and displeasure regarding the world. Thus, monks, a monk developing the four establishments of mindfulness, cultivating the four establishments of mindfulness, slants towards Nibbāna, slopes towards Nibbāna, inclines towards Nibbāna" - this should be expanded.