The Buddha goes to the bathing place near the Migārāmatupāsāda with Ānanda, bathes there, and while drying his limbs, sees Pasenadi’s elephant, Seta, coming out of the bathing place, attended by great ceremony. People, seeing him, express their wonder and admiration of the noble animal. Udāyī (Kāludāyī, according to the Commentary, AA.ii.669) who is nearby, asks the Buddha if it is only the elephant whom people praise for its bulk or do they praise other bulky things as well? They do, says the Buddha, praise all huge things — horses, bulls, snakes, trees, and men — calling them Nāgā, but really, the best Nāga is the one who commits no enormity in word or thought (āguṃ, na karoti, taṃ nāgo). Thereupon, Udāyī breaks forth into verse, praising the Buddha’s teaching, comparing the Buddha to an elephant, each limb representing a different virtue (A.iii.345 ff).

This sutta is called the Nāgopama Sutta (ThagA.ii.7).