Theravāda Vinayapiṭaka
Monks’ rules and their analysis
Monks’ Training (Sekhiya) 72
… in Anāthapiṇḍika’s monastery. Now at that time the group of six monks, going at the side of a path, taught dhamma to (someone) going along the path … “…
‘I will not teach dhamma, going at the side of a path, to (someone) going along the path (and) who is not ill,’ is a training to be observed.”
Dhamma should not be taught, going at the side of a path … if he is the first wrong-doer.