At Sāvatthī.

“What do you think, Rāhula? Is perception of sights permanent or impermanent?”

“Impermanent, sir.” …

“… perception of sounds … perception of smells … perception of tastes … perception of touches … Is perception of thoughts permanent or impermanent?”

“Impermanent, sir.” …

“Seeing this, a learned noble disciple grows disillusioned with the perception of sights, sounds, smells, tastes, touches, and thoughts. …”