[424] In how many ways are these five faculties (indriya) purified?
These five faculties are purified in fifteen ways. For one avoiding faithless persons, and frequenting, associating with, and attending upon faithful persons, and reviewing discourses that inspire confidence — in these three ways the faith faculty (saddhindriya) is purified. For one avoiding lazy persons, and frequenting, associating with, and attending upon persons of aroused energy, and reviewing the right exertions (sammappadhāna) — in these three ways the energy (vīriya) faculty (viriyindriya) is purified. For one avoiding persons of muddled mindfulness, and frequenting, associating with, and attending upon persons of established mindfulness (sati), and reviewing the establishments of mindfulness (satipaṭṭhāna) — in these three ways the mindfulness faculty (satindriya) is purified. For one avoiding unconcentrated persons, and frequenting, associating with, and attending upon concentrated persons, and reviewing the jhānas and liberations (jhānavimokkha) — in these three ways the concentration (samādhi) faculty (samādhindriya) is purified. For one avoiding persons of poor wisdom, and frequenting, associating with, and attending upon wise persons, and reviewing the profound course of knowledge (ñāṇa) — in these three ways the wisdom faculty (paññindriya) is purified. Thus, for one avoiding these five kinds of persons, frequenting, associating with, and attending upon the five kinds of persons, and reviewing the five sections of the discourses (suttantakkhandha), these five faculties are purified in these fifteen ways.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.