Saṃyuktāgama 208. [Discourse on the Eye in the Present]
Thus have I heard. At one time the Buddha was staying at Vesālī in Jīvaka’s Mango Grove.
At that time the Blessed One said to the monks: “The eye in past and future is impermanent, what to say of the eye in the present! A learned noble disciple who contemplates in this way is not concerned with the eye of the past and does not rejoice in the eye of the future. Being disenchanted with the eye in the present, he does not delight in it, becomes free from desire for it, and proceeds towards disenchantment with it.
“The ear … the nose … the tongue … the body … the mind is also like that.”
When the Buddha had spoken this discourse, hearing what the Buddha had said the monks were delighted and received it respectfully.
Just as for being impermanent, in the same way [discourses] are also to be recited for being dukkha, empty, and not self.
Just as the four discourses for the internal sense-spheres, in the same way also four discourses for the external sense-spheres, [i.e.] forms, sounds, odours, flavours, tangibles, mental objects, and four discourses for the internal and external sense-spheres are to be recited.