Cittasanto wrote:There are references to those hearing one teaching and they attained Nibbana
One reference of this sort is the story of Bāhiya in Ud 1.10
. The description given suggests that he was already quite advanced in various ways before hearing the teaching, though, so he may have already completed the earlier requisites of the gradual part of the path. It's also worth noting that the explanation of the Dhamma is a way of training, so even in this case it is not "without practice".
Ud 1.10: Bāhiya Sutta wrote:I have heard that on one occasion the Blessed One was staying near Sāvatthī at Jeta's Grove, Anāthapiṇḍika's monastery. And on that occasion Bāhiya of the Bark-cloth was living in Suppāraka by the seashore. He was worshipped, revered, honored, venerated, and given homage — a recipient of robes, alms food, lodgings, & medicinal requisites for the sick. Then, when he was alone in seclusion, this line of thinking appeared to his awareness: "Now, of those who in this world are arahants or have entered the path of arahantship, am I one?"
Then a devatā who had once been a blood relative of Bāhiya of the Bark-cloth — compassionate, desiring his welfare, knowing with her own awareness the line of thinking that had arisen in his awareness — went to him and on arrival said to him, "You, Bāhiya, are neither an arahant nor have you entered the path of arahantship. You don't even have the practice whereby you would become an arahant or enter the path of arahantship."
A third time, Bāhiya said to the Blessed One, "But it is hard to know for sure what dangers there may be for the Blessed One's life, or what dangers there may be for mine. Teach me the Dhamma, O Blessed One! Teach me the Dhamma, O One-Well-Gone, that will be for my long-term welfare & bliss."
"Then, Bāhiya, you should train yourself thus: In reference to the seen, there will be only the seen. In reference to the heard, only the heard. In reference to the sensed, only the sensed. In reference to the cognized, only the cognized. That is how you should train yourself. When for you there will be only the seen in reference to the seen, only the heard in reference to the heard, only the sensed in reference to the sensed, only the cognized in reference to the cognized, then, Bāhiya, there is no you in connection with that. When there is no you in connection with that, there is no you there. When there is no you there, you are neither here nor yonder nor between the two. This, just this, is the end of stress."
Through hearing this brief explanation of the Dhamma from the Blessed One, the mind of Bāhiya of the Bark-cloth right then and there was released from effluents through lack of clinging/sustenance. Having exhorted Bāhiya of the Bark-cloth with this brief explanation of the Dhamma, the Blessed One left.
See also Ud 5.5
which describes a "sudden drop-off only after a long stretch", which may explain Ud 1.10 quoted above.
Ud 5.5: Uposatha Sutta wrote:Just as the ocean has a gradual shelf, a gradual slope, a gradual inclination, with a sudden drop-off only after a long stretch; in the same way this Dhamma & Vinaya has a gradual training, a gradual performance, a gradual practice, with a penetration to gnosis only after a long stretch. The fact that this Dhamma & Vinaya has a gradual training, a gradual performance, a gradual practice, with a penetration to gnosis only after a long stretch: This is the first amazing & astounding quality of this Dhamma & Vinaya because of which, as they see it again & again, the monks take great joy in this Dhamma & Vinaya.