Hui-neng said, "Impermanence is the Buddha-nature. Permanence is the mind that discriminates all the various dharmas good and bad." "That's not at all what the sutra says," replied Hsing-ch'ang. "I transmit the seal of the Buddha-mind, why would I deliberately say something that is counter to the Buddha's sutras?" said Hui-neng. "The sutra preaches that the Buddha-nature is permanent, but you say it is impermanent. The sutra says all dharmas good and bad and even the mind of enlightenment are impermanent. You say they are permanent," said Hsing-ch'ang. "Those differences only deepen my doubt." …
Hui-neng said, "If the Buddha-nature were permanent, what would be the need to preach beyond that about all dharmas good and bad? Even in the passage of an entire kalpa, there would not be a single person who would ever raise the mind of enlightenment. That is why I preach impermanence, and that itself is the way of true permanence preached by the Buddha. If, on the other hand, all dharmas were impermanent, then each thing would have a selfhood and take part in birth-and-death, and there would be areas to which true permanence did not reach." ?
"Therefore, I preach permanence, and it is just the same as the meaning of true impermanence preached by the Buddha. The attachment to illusory permanence of unenlightened non-Buddhists, and the discriminations of followers of the two vehicles that take permanence as impermanence … were refuted as distorted, one-sided views by the Buddha when he expounded his complete and perfect teaching of nirvana and made explicit the teaching of true permanence, true pleasure, true self, and true purity. By relying merely on words, you now subvert their inner meaning. If you mistake the perfect and subtle words the Buddha spoke just prior to his demise as indicating nihilistic impermanence or lifeless permanence, you could get no benefit from the Nirvana Sutra, even though you read it a thousand times over."
(Platform Sutra)