[429] He was dwelling at Sāvatthī. … Then a certain bhikkhu approached the Blessed One; having approached … Sitting to one side, that bhikkhu said this to the Blessed One: "How long, venerable sir, is an eon (kappa)?"
"Long, bhikkhu, is an eon. It is not easy to reckon it thus: 'so many years,' or 'so many hundreds of years,' or 'so many thousands of years,' or 'so many hundreds of thousands of years.'"
"But is it possible, venerable sir, to make a simile?"
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.