Kiṁsukopamasutta
Atha kho aññataro bhikkhu yenaññataro bhikkhu tenupasaṅkami; upasaṅkamitvā taṁ bhikkhuṁ etadavoca: “kittāvatā nu kho, āvuso, bhikkhuno dassanaṁ suvisuddhaṁ hotī”ti? “Yato kho, āvuso, bhikkhu channaṁ phassāyatanānaṁ samudayañca atthaṅgamañca yathābhūtaṁ pajānāti, ettāvatā kho, āvuso, bhikkhuno dassanaṁ suvisuddhaṁ hotī”ti.
The Simile of the Parrot Tree
Then one mendicant went up to another mendicant and asked, “Reverend, at what point is a mendicant’s vision well purified?” “When a mendicant truly understands the origin and disappearance of the six fields of contact, at that point their vision is well purified.”