At one time when the Buddha was staying at Sāvatthī in Anāthapiṇḍika’s Monastery, Venerable Udāyī’s ex-wife became a nun. She often went to see Udāyī, and he often went to see her. And Udāyī would sit down in private alone with that nun. The monks of few desires complained and criticized him, “How can Venerable Udāyī sit down in private alone with a nun?” … “Is it true, Udāyī, that you do this?” “It’s true, sir.” The Buddha rebuked him … “Foolish man, how can you do this? This will affect people’s confidence …” … “And, monks, this training rule should be recited like this:

Final ruling ‘If a monk sits down in private alone with a nun, he commits an offense entailing confession.’”

Definitions A: whoever … Monk: … The monk who has been given the full ordination by a unanimous Sangha through a legal procedure consisting of one motion and three announcements that is irreversible and fit to stand—this sort of monk is meant in this case.