From:
Theravāda Vinaya Theravāda Collection on Monastic Law
Mahāvibhaṅga The Great Analysis
Sekhiyakaṇḍa The chapter on training
Kabaḷavagga The subchapter on mouthfuls
50. Capucapukārakasikkhāpada 50. The training rule on chomping
Tena samayena buddho bhagavā sāvatthiyaṁ viharati jetavane anāthapiṇḍikassa ārāme. At one time the Buddha was staying at Sāvatthī in the Jeta Grove, Anāthapiṇḍika’s Monastery.
Tena kho pana samayena chabbaggiyā bhikkhū capucapukārakaṁ bhuñjanti …pe… At that time the monks from the group of six made chomping sounds while eating. …
“Na capucapukārakaṁ bhuñjissāmīti sikkhā karaṇīyā”ti. “‘I will not make a chomping sound while eating,’ this is how you should train.”
Na capucapukārakaṁ bhuñjitabbaṁ. One should not make a chomping sound while eating.
Yo anādariyaṁ paṭicca capucapukārakaṁ bhuñjati, āpatti dukkaṭassa. If a monk, out of disrespect, makes a chomping sound while eating, he commits an offense of wrong conduct.
Anāpatti—There is no offense:
asañcicca …pe… if it is unintentional;
ādikammikassāti. if he is the first offender.
Dasamasikkhāpadaṁ niṭṭhitaṁ. The tenth training rule is finished.
Kabaḷavaggo pañcamo. The fifth subchapter on mouthfuls is finished.