A kind of Kālika Śruta (a category of Āgama (2) (canonical work) which can be studied only in the first and last quarter of day and night), in which is given the exposition of monastic conduct, biographical accounts and metaphysical topics. In ancient times, its study was undertaken after that of the Ācārānga Sūtra (the first Aṅga (principal canonical work)), and therefore, it is named as Uttarādhyayana.
(Nandī 78)
aṇgappabhavā jiṇabhāsiyā ya patteyabuddhasaṃvāyā.
(UNi 4)
ācārāt parataḥ pūrvakāle yasmādetāni pathitavanto yatayastena uttarādhyayanāni.
(TaBhā 1.20 Vṛ)