Theravāda Vinayapiṭaka
Monks’ rules and their analysis
Monks’ Training (Sekhiya) 49
… in Anāthapiṇḍika’s monastery. Now at that time the group of six monks ate putting out their tongues … “…
‘I will not eat putting out the tongue,’ is a training to be observed.”
One should not eat putting out the tongue … offence of wrong-doing.
There is no offence if it is unintentional … if he is the first wrong-doer.