The seventh sutta of the Majjhimanikāya (M.i.36 ff). At Sāvatthi in Anāthapiṇḍika’s monastery.

The Buddha says that, even as a dirty piece of cloth takes dyes badly, so in an impure heart bliss is not to be found. He then proceeds to enumerate the heart’s impurities and to show how they can be cleansed. Sundarika-Bhāradvāja, who is present, asks the Buddha if he has bathed in the Bāhukā. The Buddha then give s a list of places whose waters are considered holy, and declares that the real cleansing is the cleansing of the heart — “to love all that lives, speak truth, slay not nor steal, no niggard be but dwell in faith.” Bhāradvāja seeks ordination and becomes an Arahant.

This sutta that is referred to in the Sumaṅgalavilāsinī (DA.i.50, 123), as the Vattha Sutta.