For all who are familiar with Nagarjuna’s eight negations (or four pairs of negations): namely,
neither birth nor death,
neither end nor permanence,
neither identity nor difference, and
neither coming nor going.
I remember reading in an article once that these were directly traceable to some passage in the Nikayas/Agamas: it was actually quite specific–i.e., not just that the general theme was traceable. As I remember, I even saw the sutta citation.
The eight negations of Nagarjuna are the middle way of emptiness. The following books by Choong Mun-keat may be useful for you:
The Fundamental Teachings of Early Buddhism: A Comparative Study Based on the Sutranga portion of the Pali Samyutta-Nikaya and the Chinese Samyuktagama (Series: Beitrage zur Indologie Band 32; Harrassowitz Verlag, Wiesbaden, 2000), pp. 60-66, 95-96, 192-199, 239.
The Notion of Emptiness in Early Buddhism (1995; second revised edition, Motilal Banarsidass, Delhi, 1999), pp. 32-41.
If we take out the identity/difference line, the list happens to resemble passages like Paṭhamanibbānasutta Ud 8.1:
There is that dimension, monks, where there is neither earth, nor water, nor fire, nor wind; neither dimension of the infinitude of space, nor dimension of the infinitude of consciousness, nor dimension of nothingness, nor dimension of neither perception nor non-perception; neither this world, nor the next world, nor sun, nor moon. And there, I say, there is neither coming, nor going, nor staying; neither passing away nor arising: unestablished, unevolving, without support. This, just this, is the end of stress.
Thank you to all who answered. These answers all gave me some food for thought. I’m also searching for one sutra where approximately 30 or so synonyms for nibbana are given. As I remember, some were quite “sunyatish.” I can’t seem to find it at the moment, though.