The twenty fourth sutta of the Majjhima Nikáya. Sáriputta visits Punna Mantániputta in Andhavana and asks him why he lives the higher life. To attain absolute Nibbána, answers Punna, and, on being questioned further as to the nature of Nibbána, he explains that Nibbána is the goal and can only be attained by passing through various successive stages purity of life, purity of heart, purity of view, purity through dispelling doubts, purity through full insight into paths, right and wrong, into the path to be followed, and the purity which arises from insight. It may be compared to a journey of Pasenadi from Sávatthi to Sáketa, by means of relays of seven carriages.
It is said in the introduction to the sutta that Sáriputta had been awaiting the opportunity of a discussion with Punna ever since he heard the monks at Veluvana in Rájagaha speak of him to the Buddha in terms of the highest praise. But this opportunity did not arise until later, when Punna visited Sávatthi. Punna was unaware of the identity of Sáriputta until the end of his discourse (M.i.145 51).
The Mahávamsa Tíká mentions (MT.552f ) that once Ambapásánavásí Cittagutta preached this sutta to a very large assembly of monks and nuns at the Lohapásáda in Anurádhapura, and in his exposition of the sutta included a short account of the relies enshrined in the Mahá Thúpa.
It has been suggested by Dr. Neumann that the upatisapasina mentioned in Asoka's Bhabru Edict, refers to this sutta. But see Rhys Davids, J.R.A.S.1893, and Mukherji, Asoka, 118f., n.8.