A stabbing of a thumb at paper: HERE.
I heard of the Buddha that at one point in time, one of the people studying under him named Malunkya came across a bunch of questions about the universe that the Enlightened One had simply not answered in the course of his teachings. Is the universe eternal? Is the universe not eternal? Is the universe finite? Is the universe infinite? Are body and soul two entities? Are body and soul the same entity? In death, does an Enlightened One exist? Not exist? Both exist and not exist? Neither exist nor not exist? Malunkya thought about this, and got a bug in his ear-- he needed these questions answered, darnit, and he needed those answers -now-. So, one day, he goes to the Buddha, and proclaims, "If you can't answer me these questions, then I'm going to give up the study of enlightenment entirely."
"Malunkya, did I say when you came to me, 'Practice the spiritual life with me, and I will answer these questions for you?"
"No, Lord," he had to admit.
"Anyone who renounces the spiritual life until I answer these questions will surely die without my having answered them. Such a person is akin to a man who has been struck in the night by a poisoned arrow that refuses treatment until he learns the identity of his attacker. He who says 'I will not be healed until I know if it was a priest, a prince, a farmer, or a slave who shot me' is likely to go to his grave without knowing."
Is it possible the Buddha knew the answers to those questions? Sure. That he didn't know? Also sure. But more importantly, he chose not to answer because knowing the answers to those questions, answers certified-stamped by the Enlightened One, would not advance the state of the seeker in his self-cleansing.
Nibbana/nirvana is not such a thing that we can define it. Defining it provokes issues, problems, irrelevant concerns-- things anathema to understanding the nature, cause, cessation of suffering. Ghafla distractions, all. When asking a question of this nature, one must be aware of why one asks it in the first place.
That's that moment: free, wild, a first-spear in one hand and a painted shield on the other...