四分律刪繁補闕行事鈔 2.185

2.185

實得道向未具者說戒八。問：凡夫無聖，不可得犯；聖人奉戒，一制不犯，用制何為？答：制聖為遮凡。若後向說，即知是凡；為護大妄，不令有犯，豈非是要也。

Precept eight: Speaking to an unordained person when having actually attained the Path. Question: An ordinary person has no noble [attainment] and cannot commit this offense; a noble person upholds the precepts and, once prohibited, does not transgress them. What is the purpose of formulating [this precept]? Answer: Formulating it for noble ones is to prevent ordinary persons [from boasting]. If one subsequently speaks of it [to the unordained], one is known to be an ordinary person; it is meant to guard against major false speech and prevent transgression. How could it not be essential?