Reference for Berakhot 54:2

ותניא רבי אליעזר אומר המתפלל אחורי רבו והנותן שלום לרבו והמחזיר שלום לרבו והחולק על ישיבתו של רבו והאומר דבר שלא שמע מפי רבו גורם לשכינה שתסתלק מישראל

And there is a teaching: R. Eliezer says: He who prays behind his master, or greets his master or returns his salutation, or opposes [the opinions taught by] his master's school, or reports a teaching [in his master's name] which he had not heard from his master's lips, causes the Shekinah to depart from Israel !

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