[54] Now at that time several bhikkhus were traveling on the highway from Sāketa to Sāvatthī. On the way, robbers came out and robbed those bhikkhus. Then those bhikkhus, being scrupulous, thinking, "It has been prohibited by the Blessed One to ask a householder or a householder's wife who is not a relation for a robe," did not ask; and, naked just as they were, they went to Sāvatthī and paid homage to the bhikkhus. The bhikkhus said this: "Friends, these Ājīvakas are surely good ones, in that they pay homage to the bhikkhus." They said: "Friends, we are not Ājīvakas; we are bhikkhus."
The bhikkhus said this to the Venerable Upāli: "Come, friend Upāli, examine these men." Then those bhikkhus, being examined by the Venerable Upāli, informed him of the matter. Then the Venerable Upāli, having examined those bhikkhus, said this to the bhikkhus: "These are bhikkhus, friends; give them robes."
Those bhikkhus who were of few wishes … looked down upon, criticized, and denounced them, saying: "How indeed could bhikkhus come naked? Surely they should have come having covered themselves with grass?" Then those bhikkhus reported the matter to the Blessed One.
Then the Blessed One, on account of that cause, on that occasion, having given a talk on the Dhamma, addressed the bhikkhus: "Bhikkhus, I allow a bhikkhu whose robe has been stolen or whose robe has been lost to ask a householder or a householder's wife who is not a relation for a robe. At whatever residence he first arrives, if there is there a vihāra-cloth belonging to the Saṅgha, or a coverlet, or a ground-covering, or a mattress-cover, he may take that and wear it, thinking, 'When I have obtained [a robe], I shall put this back.' But if there is no vihāra-cloth belonging to the Saṅgha, nor a coverlet, nor a ground-covering, nor a mattress-cover, he should come covered with grass or with leaves; but he should certainly not come naked. Whoever should come [naked] commits an offense of wrong-doing (dukkaṭa).
"And thus, bhikkhus, you should recite this training rule (sikkhāpada): Whatever bhikkhu should ask a householder or a householder's wife who is not a relation for a robe, except on an occasion, it entails an offense of expiation with relinquishment (nissaggiya pācittiya). Herein this is the occasion: the bhikkhu is one whose robe has been stolen or whose robe has been lost — this is the occasion herein."
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.