In the First Nibbana Sutta Lord Buddha states:
There exists, monks, Nirvana as home (Ayatana), a dwelling place where there is neither earth, nor water, nor fire, nor wind, nor sphere of infinity of space, nor sphere of infinity of consciousness, nor sphere of nothingness, nor sphere of neither perception nor non-perception, nor this world, nor the next world, nor sun nor moon. I, the Tathagata, do not speak of that Ayatana as coming or going, or as remaining, falling, or arising. That Ayatana is without foundation, without occurrence, without sense-object. It is the end of suffering.
(Kh. 5/158/206-207).
Note: Ayatana means source or dwelling place meaning of country of birth (sañjatidesa), cause (hetu) and dwelling place (vasatthana). [Pali-Thai-Sanskrit Dictionary, Phrachaoborommawongthoe Kromphrachanthaburinaruenat: 25 November BE 2512, p. 122:]
In the Fourth Nibbana Sutta Lord Buddha states:
Instability [struggle due to craving and wrong view] is with one with craving and wrong view and is not with one without them. When there is no instability peaceful tranquility arises. When there is peaceful tranquility there is no sensual desire. When there is no sensual desire there is no coming-and-going. When there is no coming-and-going there is no decease-and-arising [death and rebirth]. When there is no decease-and-arising, there is neither this world nor next world nor in between the two worlds. This is the end of suffering.
(Kh. 25/161/208).
Ayatana that is Nirvana means the dwelling place [home] of the Nirvana Element or Anupadisesanibbanadhatu (Nirvana without life remaining) of the Arahants whose Five Aggregates have perished at death. Only the Nirvana Element (Dhamma that sustains the state of Nirvana) remains. It is an eternal, unconditioned Dhamma with the characteristics of the unconditioned that arising does not occur (Na uppado paññayati), passing away does not occur (Na vayo paññayati) and while it stands, changeability does not occur (Na thitassa aññathattam paññayati).
Some teachers believe that Nirvana is Non-self and Ayatana Nirvana does not mean a place. This is stated in the second footnote of the Thai Tipitaka B.E. 2549:
Ayatana is Nirvana. Here Lord Buddha calls Nirvana an Ayatana because it is a causal object. It is the cause of path and fruit knowledge. This is like calling form a domain of Ayatana (Rupayatana) because form is the causal object of eye consciousness [Khu. p.407]. It does not mean a land or a place.
The learned (the Perfect Ones or Arahants) must get rid of doubt by carefully studying, practicing and developing wisdom (Pañña) through reading, reflecting and meditation to see and realize both conditioned and unconditioned Dhammas and the Four Noble Truths. They must know, see and become the Nirvana Element (Nibbanadhatu) for themselves. This Dhamma is to be directly experienced by oneself. Do not waste time arguing with others. You can personally experience valid and reliable proof that Ayatana Nirvana is the home of the Nirvana Element, as realized and testified to by the Noble Ones.
In the Second Nibbana Sutta, Lord Buddha says that Truth (Sacca) is Nirvana, the Nirvana Element and Ayatana Nirvana that is seen by the Noble Ones (Arahants), but is difficult for the ordinary person to see:
Truth (Sacca) or Nirvana is a natural phenomena that is hard to see. It is without struggle or craving. It is not easy to see. Only those who have abandoned craving and defilements can know it and see it.
(Kh. 25/159/207).