[452] Thus have I heard. On one occasion the Blessed One was dwelling near Mithilā, in the Maghadeva Mango Grove. Then the Blessed One displayed a smile at a certain spot. Thereupon this thought occurred to the venerable Ānanda: "What now is the cause, what is the reason, for the Blessed One's display of a smile? Tathāgatas do not display a smile without a reason." Then the venerable Ānanda, having arranged his robe over one shoulder and raised his joined palms in reverence toward the Blessed One, said to the Blessed One: "What now, venerable sir, is the cause, what is the reason, for the Blessed One's display of a smile? Tathāgatas do not display a smile without a reason."
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.