Hello as far as I am concerned this performing Vinaya funtions together is common knowledge I searched to internet for a source and found the following so it is best that we take to heart the writings of the Chinese pilgrims who visited India centuries ago They reported that even after the early Buddhists had split into 18 schools each with its own Tripitaka and Patimokkha and the Mahayanists had added their texts to the tradition bhikkhus belonging to different schools could be found living together in the same monastery practicing and conducting communal business in peace and harmony Buddhist Monastic Code I Thanissaro bhikkhu So I guess it can be found in one of the accounts of the Chinese pilgrims I think it is mentioned in Lamotte s book also Did you know there is actually a precedent set in the Buddha s time about adding new rules by the Sangha One local Sangha monastery added a new pacittiya offence after which the Buddha admonished them and said that this can only be done by himself So at the First Buddhist Council it was not necessary to close the Patimokkha since it was never open to the Sangha anyway They did decide not to relinquish the lesser and minor rules though This story of the Buddha s time might explain why they added only sekhiyas to the various patimokkhas afterwards Greetings