Reference for Moed Katan 33:20
אמר רב גידל אמר רב ת"ח מנדה לעצמו ומיפר לעצמו אמר רב פפא תיתי לי דלא שמיתי צורבא מרבנן מעולם אלא כי קא מיחייב צורבא מרבנן שמתא היכי עביד כי הא דבמערבא מימנו אנגידא דצורבא מרבנן ולא מימנו אשמתא
Said R'Giddal, as citing Rab: 'A scholar-disciple may Pronounce "separation" on himself and absolve himself'. Said R'Papa, 'May [good] befall me, for I have never put the shammetha on any Collegiate.'<span class="x" onmousemove="('comment',' Some take it as an asseveration, 'May evil befall me if I ever did that'. Cf. II Sam. III, 35.');"><sup>26</sup></span> But then, when a Collegiate did incur the shammetha, how did he act? - As they do [in the West]; for in the West [Palestine] they appoint a tribunal for chastising a Collegiate but do not appoint a tribunal for pronouncing a shammetha.