Thus have I heard. At one time the Lord was staying near Savatthi in the Jeta Wood at Anathapindika's monastery. On that occasion the Lord was instructing... the bhikkhus with a Dhamma talk connected with Nibbana, and those bhikkhus... were intent on listening to Dhamma.
Then, on realizing its significance, the Lord uttered on that occasion this inspired utterance:
There is, bhikkhus, a not-born, a not-brought-to-being, a not-made, a not-conditioned. If, bhikkhus, there were no not-born, not-brought-to-being, not-made, not-conditioned, no escape would be discerned from what is born, brought-to-being, made, conditioned. But since there is a not-born, a not-brought-to-being, a not-made, a not-conditioned, therefore an escape is discerned from what is born, brought-to-being, made, conditioned. (Udana 8,3)