Dhammakathikapucchasutta
Atha kho aññataro bhikkhu yena bhagavā tenupasaṅkami …pe… ekamantaṁ nisinno kho so bhikkhu bhagavantaṁ etadavoca: “‘dhammakathiko, dhammakathiko’ti, bhante, vuccati. Kittāvatā nu kho, bhante, dhammakathiko hotī”ti?
A Dhamma Speaker
Then a mendicant went up to the Buddha … and asked him, “Sir, they speak of a ‘Dhamma speaker’. How is a Dhamma speaker defined?”