Aṅguttara Nikāya,
Catukkanipātapāḷi
Satipaṭṭhānasuttaṃ
AN4.274
'Of passion, almsmen, for getting acquainted with, four principles should be cultivated.
Which four?
Here, almsmen, an almsman looking into body dwells in body as the ardent aware meditator would remove the avarice and distress about the world.
Looking into feelings dwells in feelings as the ardent aware meditator would remove the avarice and distress about the world.
Looking into mind dwells in mind as the ardent aware meditator would remove the avarice and distress about the world.
Looking into principles dwells in principles as the ardent aware meditator would remove the avarice and distress about the world.
Of passion, almsmen, for getting acquainted with, these four principles should be cultivated.'