[403] Thus have I heard:
On one occasion the Blessed One was wandering on tour among the Kosalans together with a large Saṅgha of bhikkhus. Then the Blessed One stepped off the road and, at a certain spot, displayed a smile. Then it occurred to the Venerable Ānanda: "What is the cause, what is the reason, for the Blessed One's displaying a smile? Tathāgatas do not display a smile without a reason." Then the Venerable Ānanda arranged his upper robe over one shoulder, extended his joined palms in reverence toward the Blessed One, and said to the Blessed One: "Venerable sir, what is the cause, what is the reason, for the Blessed One's displaying a smile? Tathāgatas do not display a smile without a reason."
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.