SN 29.6

Catutthauposathasutta

Sāvatthinidānaṁ. Ekamantaṁ nisinno kho so bhikkhu bhagavantaṁ etadavoca: “ko nu kho, bhante, hetu, ko paccayo, yena m’idhekacce opapātikā nāgā uposathaṁ upavasanti vossaṭṭhakāyā ca bhavantī”ti?

Sabbath (4th)

At Sāvatthī. Seated to one side, that mendicant said to the Buddha: “Sir, what is the cause, what is the reason why some spontaneously-born dragons keep the sabbath, having transformed their bodies?”

“Idha, bhikkhu, ekaccānaṁ opapātikānaṁ nāgānaṁ evaṁ hoti: ‘mayaṁ kho pubbe kāyena dvayakārino ahumha, vācāya dvayakārino, manasā dvayakārino. Te mayaṁ kāyena dvayakārino, vācāya dvayakārino, manasā dvayakārino, kāyassa bhedā paraṁ maraṇā opapātikānaṁ nāgānaṁ sahabyataṁ upapannā. Sacajja mayaṁ kāyena sucaritaṁ careyyāma, vācāya … manasā sucaritaṁ careyyāma, evaṁ mayaṁ kāyassa bhedā paraṁ maraṇā sugatiṁ saggaṁ lokaṁ upapajjeyyāma. Handa mayaṁ etarahi kāyena sucaritaṁ carāma, vācāya … manasā sucaritaṁ carāmā’ti. Ayaṁ kho, bhikkhu, hetu, ayaṁ paccayo, yena m’idhekacce opapātikā nāgā uposathaṁ upavasanti vossaṭṭhakāyā ca bhavantī”ti.

“Mendicant, it’s when some spontaneously-born dragons think: ‘In the past we did both kinds of deeds by body, speech, and mind. When the body broke up, after death, we were reborn in the company of the spontaneously-born dragons. If today we do good things by body, speech, and mind, when the body breaks up, after death, we may be reborn in a good place, a heavenly realm. Come, let us do good things by way of body, speech, and mind.’ This is the cause, this is the reason why some spontaneously-born dragons keep the sabbath, having transformed their bodies.”