Saṃyuktāgama 220. [Second Discourse on the Path to Nirvāṇa]
Thus have I heard. At one time the Buddha was staying at Sāvatthī in Jeta’s Grove, Anāthapiṇḍika’s Park.
At that time the Blessed One said to the monks: “There is a path leading to Nirvāṇa. What is the path leading to Nirvāṇa? Contemplate the eye as not-self. Contemplate also forms, eye-consciousness, and feeling arisen in dependence on eye-contact that is experienced within, be it painful, pleasant, or neutral, as being not-self.
“The ear … the nose … the tongue … the body … the mind is also like that. This is called the path leading to Nirvāṇa.”
When the Buddha had spoken this discourse, hearing what the Buddha had said the monks were delighted and received it respectfully.