This was said by the Buddha, the Perfected One: that is what I heard. Vuttañhetaṁ bhagavatā vuttamarahatāti me sutaṁ:

“Enjoy retreat, mendicants, love retreat. Be committed to inner serenity of the heart, don’t neglect absorption, be endowed with discernment, and frequent empty huts. “Paṭisallānārāmā, bhikkhave, viharatha paṭisallānaratā, ajjhattaṁ cetosamathamanuyuttā, anirākatajjhānā, vipassanāya samannāgatā, brūhetāro suññāgārānaṁ. A mendicant who enjoys retreat can expect one of two results: Paṭisallānārāmānaṁ, bhikkhave, viharataṁ paṭisallānaratānaṁ ajjhattaṁ cetosamathamanuyuttānaṁ anirākatajjhānānaṁ vipassanāya samannāgatānaṁ brūhetānaṁ suññāgārānaṁ dvinnaṁ phalānaṁ aññataraṁ phalaṁ pāṭikaṅkhaṁ—enlightenment in this very life, or if there’s something left over, non-return.” diṭṭheva dhamme aññā, sati vā upādisese anāgāmitā”ti.

The Buddha spoke this matter. Etamatthaṁ bhagavā avoca. On this it is said: Tatthetaṁ iti vuccati:

“With minds at peace, alert, “Ye santacittā nipakā, mindful and meditative, satimanto ca jhāyino; they rightly discern the Dhamma, Sammā dhammaṁ vipassanti, unconcerned for sensual pleasures. kāmesu anapekkhino.

Delighting in diligence, peaceful, Appamādaratā santā, seeing fear in negligence, pamāde bhayadassino; such a one can’t decline, Abhabbā parihānāya, and has drawn near to extinguishment.” nibbānasseva santike”ti.

This too is a matter that was spoken by the Blessed One: that is what I heard. Ayampi attho vutto bhagavatā, iti me sutanti.

Aṭṭhamaṁ.