Where is Nibbana/Nirvana being Unconditioned stated in the Canon?

So I realized I have been far too harsh in judging Theravada Buddhism in the doctrine of unconditionality. I was asking my Mahayana teacher whether unconditionality is one of those deluded "confused imagination" described in the Heart Sutra. She replied: to not reach the unconditionality is to have "confused imagination". I was stunned by the answer and decide to do some reflecting. What could be unconditional?

Then I made a realization, the Dharma, that is the Law, the Truth of Four Noble Truths, Dependent Origination, Impermanence, Emptiness are unconditional. Truth itself is unchanging. Change itself is unchanging. Impermanence is permanent. Certainly how we perceive and experience truth is changing and conditional, but it remain the Truth no matter whether anyone realize it or not.

With this in mind, we can surmised that Nirvana is unconditional as the Truth of Cessation of Suffering. If we have made the complete realization of Nirvana, we would be able to end any suffering that may arise. This would correspond well in line of the cultivation of wisdom factor of the Noble Eightfold Path. The subjective experience of this truth is conditional, but the Truth itself was always present.

In fact, it would appears that this doctrine is in contradiction with the doctrine of dependent origination. [...] I believe the reasoning is as follows ...

It seems you are conflating causes and conditions as if they were the same? For example, it's not true that a certain thing ceases when it's cause ceases -- not in Buddhism and not in the real world. Causality, strictly speaking, is a very subtle subject, and Buddhism approach it mostly through moral karma.

The subject in discussion, however, is not really causality, but conditionality. It's conditionality that dependent origination (D.O) deals with:

When this is, that is.
From the arising of this comes the arising of that.
When this isn't, that isn't.
From the cessation of this comes the cessation of that.

Consider a person who lights a candle. What caused the fire to light up? This is a very difficult question. Was it the person? The lighter? His parents who gave him birth? Certainly not the candle wick.

But it's the candle wick (or generally, the fuel) in the Buddha's analogies, that stands for the condition for the fire to keep burning. In other words, that which, when present, keeps the flame going, and when absent, have the fire to cease -- that's the Buddha strategy for closing up on the problem of dukkha. Not the events that led the flame to become (e.g. the person lighting it up), nor the events that led the fire to cease (e.g. water thrown at it).

In D.O. terms, the sense of vision does not arise when there is not a healthy organ like an eye. Simply as that. But when eye is present, and eye-consciousness is present, and forms are present, contact is subject to arising. With the absence of any of the three, say, any present contact cease and there is no possibility for a new contact to arise.

Thus, provided that dukkha is dependent (not caused by) craving and D.O. holds, if one finds a way to cease craving without reminder, than dukkha won't ever find support again. The question then, is whether or not one believes it's possible to cease craving without reminder. But it should be clear that if the relations hold, there's no possibility for dukkha to rise again.

Whether Nirvana is "caused" by the practitioner practicing or not, and what this says about Nirvana is irrelevant -- the "unconditional" quality that buddhists refer to and assign to Nirvana has no relation to this "causality", after all.

To further illustrate, if we apply the same reasoning of "causes as conditions" you gave to show that Nirvana is conditioned, we can reach even more absurd conclusions. For example, are our parents the cause we were born? Then, according to D.O., should we fall on the ground and die as soon as our parents die? Or is our birth caused by their intercourse? So, should we have ceased to be as soon as they stopped that intercourse as per D.O.? If what caused me to know arithmetic is studying, should I forget everything about it once I take a break? And so on...

“There is, monks, an unborn, unbecome, unmade, unconditioned. If, monks there were not that unborn, unbecome, unmade, unconditioned, you could not know an escape here from the born, become, made, and conditioned. But because there is an unborn, unbecome, unmade, unconditioned, therefore you do know an escape from the born, become, made, and conditioned.”

The circularity is just in appearance due to language habits. For instance, if we understand the Buddha was providing a justification for something, say, for the question "how can we know there's an escape?". In this case, then we are trapped by the options he gave and we might end up making the circular reasoning with what has been offered. However, he is just stating some simple propositions and relations:

• There's X.
• With X being, we can do Y.
• If there wasn't X, we could not do Y.

...which, by the way, has the same format of D.O.

Nirvana is (in Chinese) 常樂我凈, the English term "Unconditional" trying to convey this 常 meaning is insufficient and prone to lead to wrong understanding thus wrong view. There are too many incorrect terms with the similar problems, spreading via the English media, it would be horrible to see into the future how this trend has led to the decline finally destruction of Buddha's authentic teachings. The decline may be symptomized a short-lived sudden glistening for it caught the world's attention by conversing in English. The Pali Canon I tried hard to read some but it's so repetitive so painful to read. Those I read from the online sources and sometimes I read from this forum the quotes are so plank I can't extract any "juice" from the words, maybe they are in fact so sophisticated that's beyond my understanding, maybe, maybe, I don't know.

All conditioned things have an arising, ceasing, and turning otherwise characteristics.

Nibbana does not have these marks.

http://seeingthroughthenet.net/wp-content/uploads/2016/12/The-Law-of-Dependent-Arising_LE_Rev_1.0.pdf

At page 348 this is said with copious quotes from Pali.

The path is conditioned:

Monks, among all things conditioned, the Noble Eightfold Path is reckoned to be the best of them all. Those who have faith in the Noble Eightfold Path have faith in the best; and for those who have faith in the best, the best result will be theirs. AN 4:34

The destination is unconditioned:

Monks, among things conditioned and unconditioned, dispassion is reckoned to be the best of them all: the crushing of all infatuation, the removal of thirst, the uprooting of attachment, the cutting off of the round, the destruction of craving, dispassion, Nibbāna. Those who have faith in the Dhamma of dispassion have faith in the best; and for those who have faith in the best, the best result will be theirs. AN 4:34

---

There is, monks, an unborn, unbecome, unmade, unconditioned. If, monks there were not that unborn, unbecome, unmade, unconditioned, you could not know an escape here from the born, become, made, and conditioned. But because there is an unborn, unbecome, unmade, unconditioned, therefore you do know an escape from the born, become, made, and conditioned. Ud 8.3

For example, a fire burns conditioned by wood. The same fire is extinguished, by using water. Using water to extinguish the fire is conditoned. But what remains, namely, the absence of fire, is not conditioned by the water because it is not dependent upon the water. When the fire is extinguished, the subsequent evaporation or absence of the water is not the condition for the absence of fire. The fire had a cause (e.g. lightning striking a tree); the extinguishing of the fire had a cause (e.g. hosing with water) but the staying out of the fire is not conditioned by the water. It is the absence of fire that is Nibbana.

The path removes what is hidden. But the path does not create or cause what is hidden.

Similarly, cutting down a tree is dependent upon (conditioned by) an axe. But once tree is cut down, what remains is not dependent upon the axe. Thus what remains is 'unconditioned' since what remains has always been there but the tree covered what was always already there.

Bhikkhus, this bhikkhu is called one whose cross-bar has been lifted, whose trench has been filled in, whose pillar has been uprooted, one who has no bolt, a noble one whose banner is lowered, whose burden is lowered, who is unfettered.

And how is the bhikkhu one whose cross-bar has been lifted? Here the bhikkhu has abandoned ignorance, has cut it off at the root, made it like a palm stump, done away with it, so that it is no longer subject to future arising. That is how the bhikkhu is one whose cross-bar has been lifted.

And how is the bhikkhu one whose trench has been filled in? Here the bhikkhu has abandoned the round of births that brings renewed being, has cut it off at the root…so that it is no longer subject to future arising. That is how the bhikkhu is one whose trench has been filled in.

And how is the bhikkhu one whose pillar has been uprooted? Here the bhikkhu has abandoned craving, has cut it off at the root…so that it is no longer subject to future arising. That is how the bhikkhu is one whose pillar has been uprooted.

And how is the bhikkhu one who has no bolt? Here the bhikkhu has abandoned the five lower fetters, has cut them off at the root…so that they are no longer subject to future arising. That is how the bhikkhu is one who has no bolt.

And how is the bhikkhu a noble one whose banner is lowered, whose burden is lowered, who is unfettered? Here a bhikkhu has abandoned the conceit ‘I am,’ has cut it off at the root so that it is no longer subject to future arising. That is how the bhikkhu is a noble one whose banner is lowered, whose burden is lowered, who is unfettered.

Bhikkhus, when the gods with Indra, with Brahmā and with Pajāpati seek a bhikkhu who is thus liberated in mind, they do not find anything of which they could say: ‘The consciousness of one thus gone is supported by this.’ Why is that? One thus gone, I say, is untraceable here and now.

MN 22