I've just been doing a little work of the three punnakiriyavatthus,
the famous dana, sila, bhavana, and find myself surprised how little
these occur in the suttas. I have references at AN8.36 (! in the
eights, not the threes), and the Sangiti Sutta. I don't think there is
anywhere in the Nikayas that actually explains them - but where in the
Pali tradition do we find explanations, and what are they, especially
bhavana?
I have compared with a sutta in the Chinese Ekottara, where they are
indeed explained, much as one would expect: bhavana is the 7
bojjhangas.