Theravāda Vinayapiṭaka
Monks’ rules and their analysis
Monks’ Training (Sekhiya) 50
… in Anāthapiṇḍika’s monastery. Now at that time the group of six monks ate smacking the lips … “…
‘I will not eat smacking the lips,’ is a training to be observed.”
One should not eat smacking the lips … if he is the first wrong-doer.
The Fifth Division: that on the mouthful