[869] Origin at Sāvatthī. Now at that time the group-of-six bhikkhus, sitting on the ground, taught the Dhamma to a person seated on a seat. …
"I shall not, sitting on the ground, teach the Dhamma to a person who is not ill and who is seated on a seat" — this is a training to be observed.
The Dhamma should not be taught by one sitting on the ground to a person who is not ill and who is seated on a seat. Whatever bhikkhu, out of disrespect, sitting on the ground, teaches the Dhamma to a person who is not ill and who is seated on a seat, commits an offence of wrong-doing (dukkaṭa).
There is no offence: if it is unintentional; if it is done without mindfulness; if he does not know; if the person is ill; in emergencies; if he is insane; if he is the first offender.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.