At Devadaha
Devadaha Sutta  (SN 35:134)

On one occasion the Blessed One was staying among the Sakyans near a Sakyan town named Devadaha. There he addressed the monks, “Monks, I don’t say of all monks that they have work to do with heedfulness with regard to the six contact-media. But I don’t say of all monks that they don’t have work to do with heedfulness with regard to the six contact-media.

“Those monks who are arahants—whose effluents are ended, who have reached fulfillment, done the task, laid down the burden, attained the true goal, laid to waste the fetter of becoming, and who are released through right gnosis: Of them I say that they don’t have work to do with heedfulness with regard to the six contact-media. Why is that? They have completed their work with heedfulness. They are incapable of falling back.

“But as for those monks who are in training,1 who have not attained the heart’s goal but remain intent on the unsurpassed safety from bondage: Of them I say that they still have work to do with heedfulness with regard to the six contact-media. Why is that?

“There are forms cognizable via the eye that are agreeable & disagreeable. [When one is heedful] they don’t persist in consuming the mind, even when contacted again & again. When awareness isn’t consumed, persistence is aroused & untiring, the mind concentrated & gathered into singleness. Seeing this fruit of heedfulness, I say of those monks that they still have work to do with heedfulness with regard to the six contact-media.

“There are sounds cognizable via the ear… aromas cognizable via the nose… flavors cognizable via the tongue… tactile sensations cognizable via the body…

“There are ideas cognizable via the intellect that are agreeable & disagreeable. [When one is heedful] they don’t persist in consuming the mind, even when contacted again & again. When awareness isn’t consumed, persistence is aroused & untiring, the mind concentrated & gathered into singleness. Seeing this fruit of heedfulness, I say of those monks that they still have work to do with heedfulness with regard to the six contact-media.”

Note

1. A monk who has attained at least stream-entry, but who has yet to achieve arahantship. Of course, a monk who has not yet reached stream-entry has even more reason to be heedful in the ways recommended here.

See also: DN 16; SN 3:17; SN 35:97; SN 55:40; AN 6:31; AN 10:15; Iti 16–17