Kiṁsukopamasutta

sn35.245:1.1 Then one mendicant went up to another mendicant and asked,

sn35.245:1.2 “Reverend, at what point is a mendicant’s vision well purified?”

sn35.245:1.3 “When a mendicant truly understands the origin and disappearance of the six fields of contact, at that point their vision is well purified.”