[147] Bhikkhus, these four times, when rightly developed and rightly kept rolling on, gradually lead to the destruction of the taints (āsava). What four? Listening to the Dhamma at the proper time, discussion of the Dhamma at the proper time, serenity (samatha) at the proper time, and insight (vipassanā) at the proper time. These four times, bhikkhus, when rightly developed and rightly kept rolling on, gradually lead to the destruction of the taints.
Just as, bhikkhus, when the sky rains down in heavy drops upon a mountaintop, the water, flowing down according to the slope, fills the mountain clefts, gullies, and creeks; the mountain clefts, gullies, and creeks, being full, fill up the small pools; the small pools, being full, fill up the large pools; the large pools, being full, fill up the small rivers; the small rivers, being full, fill up the great rivers; the great rivers, being full, fill up the ocean, the great sea — even so, bhikkhus, these four times, when rightly developed and rightly kept rolling on, gradually lead to the destruction of the taints.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.