Ud 8.1 Paṭhama Nibbānapaṭisaṁyutta Sutta: The First Discourse About Nibbāna
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… no coming or going or remaining or passing away or reappearing. It is not established, does not proceed, and has no support. Just this is the end of suffering.
The nature of Nibbāna especially as differentiated from the (other) attainments of Samādhi.