The eighth sutta of the Digha Nikāya. It consists of a dialogue between the Buddha and Acela-Kassapa on self-mortification, and contains an account of some of the practices prevalent among the ājīvakas.
The Buddha claims that the insight and self-control and self-mastery of the arahant are much harder of attainment than the merely physical practices of the ascetics, which are far more evident to the vulgar. The Buddha states that self-mortification is an actual hindrance to spiritual development, for it turns a man's mind from more essential matters.
It is said that at the conclusion of the Sutta, Kassapa entered the Order and, in due course, became an arahant. D.i.161-77.