He became an Arahant while crossing the ocean in a boat.
"Contemplating the Abhidhamma:
For monks who are masters of the Abhidhamma too, as [they contemplate] the classification of aggregates (khandhantara ), the classification of sense bases (āyatanantara ), the classification of elements (dhātvantara), the classification of faculties (indriyantara ), the classification of powers, enlightenment factors, kamma and result (balabojjhaṅgakammavipākantara ), the analysis of the material and immaterial—the subtle, fine phenomena—[they think:] “Our Teacher, indeed, analyzing phenomena material and immaterial, dividing them into section after section, portion after portion, as if stringing together star-forms in the sky, has shown [this to us].”
- For monks who contemplate the Abhidhamma Piṭaka, infinite joy and rapture arise. Regarding the arising of this [joy], its origin story should also be understood:
The Elder Tissadatta of the Great Fear (Mahagatimbayatissadattatthero ), thinking, “I will pay homage to the Great Bodhi tree,” while going to the far shore, seated in the boat on the surface of the water, looked out at the great ocean. At that time, for him, neither the far shore nor the near shore was discernible. But the great ocean, covered with water-particles rising up from the breaking of the waves, appearing like a spread-out silver sheet or like a scattering of flowers, was clearly visible.
He thought: “Now, is the force of the ocean’s waves strong, or is the method-approach (nayamukha) in the twenty-four divisions of the Samantapaṭṭhāna strong?”
Then, for him, the limit of the great ocean became apparent. For this [ocean] is bounded below by the earth, above by the sky, on one side by the Cakkavāḷa mountain, and on one side by the shore. But for the Samantapaṭṭhāna , no limit is discernible.
- As he contemplated the subtle and refined Dhamma, strong joy arose. He suppressed that joy, developed insight, and while sitting right there, destroyed all defilements and established himself in the supreme fruit, Arahantship. He then uttered this inspired utterance (udāna ):
“The profound in meaning, very hard to understand,
Which he, the Great Seer, having fully known by himself,
With its causes and origin, taught in full according to order —
This Dhamma he sees as if in visible form.”This is called the Ocean of Method (nayasāgara )."
—Buddhaghosa’s Atthasālinī (commentary on the Dhammasaṅgaṇī), PTS edition by E. Müller, 1897, (AI translation)
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