Sāsapasutta
Sāvatthiyaṁ viharati. Atha kho aññataro bhikkhu yena bhagavā …pe… ekamantaṁ nisinno kho so bhikkhu bhagavantaṁ etadavoca: “kīvadīgho nu kho, bhante, kappo”ti? “Dīgho kho, bhikkhu, kappo. So na sukaro saṅkhātuṁ ettakāni vassāni iti vā …pe… ettakāni vassasatasahassāni iti vā”ti.
A Mustard Seed
At Sāvatthī. Then a mendicant went up to the Buddha … and asked him, “Sir, how long is an eon?” “Mendicant, an eon is long. It’s not easy to calculate how many years, how many hundreds or thousands or hundreds of thousands of years it lasts.”