Trường Bộ Kinh (Digha Nikaya) 1:1315
SUJATOYathā kho panānanda, etarahi bhikkhū aññamaññaṁ āvusovādena samudācaranti, na kho mamaccayena evaṁ samudācaritabbaṁ.
After my passing, mendicants ought not address each other as ‘reverend’, as they do today.