sn.45.164 Saṁyutta Nikāya (Linked Discourses)

“Bhikkhus, there are these three kinds of existence. What three? Sense-sphere existence, form-sphere existence, formless-sphere existence. These are the three kinds of existence. The Noble Eightfold Path is to be developed for direct knowledge of these three kinds of existence, for the full understanding of them, for their utter destruction, for their abandoning.”