妙法蓮華經玄義 6.106

6.106

優陀那者，有法佛必應說，而無有問者，佛略開問端。如佛在舍婆提毘舍佉堂上，陰地經行，自說優陀那。所謂無我、無我所，是事善哉！是名優陀那。又如般若中，諸天子讚須菩提所說，善哉！善哉！希有世尊，難有世尊，是名優陀那。乃至佛滅後，諸弟子抄集要偈，諸無常偈作〈無常品〉，乃至〈婆羅門品〉，皆名優陀那也。

As for *udāna*, when there is a Dharma the Buddha must preach, yet no one asks, the Buddha briefly opens the topic. For instance, when the Buddha was on the upper floor of the Viśākhā hall in Śrāvastī, walking in the shade, he uttered an *udāna* himself, saying, 'No self and no mine—how excellent this is!' This is named an *udāna*. Moreover, as in the *Prajñāpāramitā*, where the devaputras praised what Subhūti had spoken, saying: 'Excellent! Excellent! Rare, O World-Honoured One! Hard to encounter, O World-Honoured One!'—this is named an *udāna*. Furthermore, after the Buddha's parinirvāṇa, the disciples compiled essential verses, taking the verses on impermanence to make the 'Chapter on Impermanence', and so on down to the 'Chapter on the Brāhmaṇa'—these are all named *udāna*.