With Udāyin
Udāyī Sutta  (SN 35:193)

On one occasion Ven. Ānanda and Ven. Udāyin were staying near Kosambī at Ghosita’s monastery. Then Ven. Udāyin, emerging from his seclusion in the evening, went to Ven. Ānanda and exchanged courteous greetings with him. After an exchange of friendly greetings & courtesies, he sat to one side. As he was sitting there, he said to Ven. Ānanda, “In many ways the body has been pointed out, revealed, and announced by the Blessed One (with these words): ‘For this reason the body is not-self.’ Can consciousness in the same way be declared, taught, described, set forth, revealed, explained, & made plain (with these words): ‘For this reason consciousness is not-self’?”

“It can… Doesn’t eye-consciousness arise in dependence on the eye & forms?”

“Yes, friend.”

“And if the cause & reason for the arising of eye-consciousness were to cease totally everywhere, totally in every way without remainder, would eye-consciousness be discerned?”

“No, friend.”

“It’s in this way, friend, that consciousness has been pointed out, revealed, and announced by the Blessed One: ‘For this reason consciousness is not-self.’

“Doesn’t ear-consciousness arise in dependence on the ear & sounds?” …

“Doesn’t nose-consciousness arise in dependence on the nose & aromas?” …

“Doesn’t tongue-consciousness arise in dependence on the tongue & flavors?” …

“Doesn’t body-consciousness arise in dependence on the body & tactile sensations?” …

“Doesn’t intellect-consciousness arise in dependence on the intellect & ideas?”

“Yes, friend.”

“And if the cause & reason for the arising of intellect-consciousness were to cease totally everywhere, totally in every way without remainder, would intellect-consciousness be discerned?”

“No, friend.”

“It’s in this way, friend, that consciousness has been pointed out, revealed, and announced by the Blessed One: ‘For this reason consciousness is not-self.’

“It’s just as if a man going around wanting heartwood, seeking heartwood, searching for heartwood, would take a sharp ax and enter a forest. There he would see a large banana tree trunk: straight, young, without shoots. He would cut off the root, cut off the crown, and unfurl the coil of the stem. There he wouldn’t even find softwood, much less heartwood.

“In the same way, a monk assumes neither a self nor anything pertaining to a self in the six media of contact. Assuming in this way, he doesn’t cling to anything in the world. Not clinging, he is not agitated. Unagitated, he is totally unbound right within. He discerns that ‘Birth is ended, the holy life fulfilled, the task done. There is nothing further for this world.’”

See also: SN 22:95; SN 35:93