Majjhima Nikaya 2:90
SUJATOKathañca, bhikkhave, bhikkhu citte cittānupassī viharati?
And how does a mendicant meditate observing an aspect of the mind?
Kathañca, bhikkhave, bhikkhu citte cittānupassī viharati?
And how does a mendicant meditate observing an aspect of the mind?