Preached at Vesāli to Sunakkhatta, before he joined the Order.
He asks the Buddha if the monks have really won all they profess or if some of them are extravagant in their professions. The Buddha explains that some of the monks are worldly, their hearts set on material things; others are free from worldly bondage, their hearts set on permanence; yet others on various jhānas; while the last have their hearts set on nibbāna; all these will act according to their beliefs.
The Buddha then explains further, using the simile of a surgeon: a patient is wounded by a poisoned arrow, even when the surgeon has removed the poison the patient must go slowly till the wound is healed. Craving is the arrow; the wound represents the six sense organs within; ignorance is the poison; mindfulness is the surgeon's probing; Noble Understanding is the surgeon's knife; and the Tathāgata the surgeon.
M.ii.252-61.