Today is Parinirvana Day–the Buddhist holiday that marks the death of the Buddha. The Ranjung Yeshe Wiki describes Parinirvana this way:
The expression “final nirvāṇa” (Skt. parinirvāṇa) refers specifically to the passing away of buddhas, such as Śākyamuni, and it is considered to be the last of the twelve principal deeds demonstrated by the buddha-body of emanation, exemplified by the death of Śākyamuni at Kuśinigara. In general, nirvāṇa is the state of total cessation of all sufferings, dissonant mental states and also of the psychological tendencies and imprints which cause our dualistic perceptions and lead sentient beings to a state of confusion within cyclic existence.
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[Parinirvana is both] the final entry into nirvana [as well as the] honorific term for the passing away of a buddha or a fully accomplished master.
Here is a selection from the Maha-parinibbana Sutta, translated from the Pali by Sister Vajira and Francis Story, which recounts the final teaching of the Buddha as he passed into Parinirvana:
Then the Blessed One addressed the bhikkhus, saying: “It may be, bhikkhus, that one of you is in doubt or perplexity as to the Buddha, the Dhamma, or the Sangha, the path or the practice. Then question, bhikkhus! Do not be given to remorse later on with the thought: ‘The Master was with us face to face, yet face to face we failed to ask him.’”
But when this was said, the bhikkhus were silent. And yet a second and a third time the Blessed One said to them: “It may be, bhikkhus, that one of you is in doubt or perplexity as to the Buddha, the Dhamma, or the Sangha, the path or the practice. Then question, bhikkhus! Do not be given to remorse later on with the thought: ‘The Master was with us face to face, yet face to face we failed to ask him.’”
And for a second and a third time the bhikkhus were silent. Then the Blessed One said to them: “It may be, bhikkhus, out of respect for the Master that you ask no questions. Then, bhikkhus, let friend communicate it to friend.” Yet still the bhikkhus were silent.
And the Venerable Ananda spoke to the Blessed One, saying: “Marvellous it is, O Lord, most wonderful it is! This faith I have in the community of bhikkhus, that not even one bhikkhu is in doubt or perplexity as to the Buddha, the Dhamma, or the Sangha, the path or the practice.”
“Out of faith, Ananda, you speak thus. But here, Ananda, the Tathagata knows for certain that among this community of bhikkhus there is not even one bhikkhu who is in doubt or perplexity as to the Buddha, the Dhamma, or the Sangha, the path or the practice. For, Ananda, among these five hundred bhikkhus even the lowest is a stream-enterer, secure from downfall, assured, and bound for enlightenment.”
And the Blessed One addressed the bhikkhus, saying: “Behold now, bhikkhus, I exhort you: All compounded things are subject to vanish. Strive with earnestness!”
This was the last word of the Tathagata.