佛說佛名經 19.18

19.18

「若式叉摩那、沙彌、沙彌尼，懺悔根本重罪，當對四清淨比丘、比丘尼，如上法滿二十一日當知清淨，除不至心。

“If a śikṣamāṇā, śrāmaṇera, or śrāmaṇerī repents of fundamental grave offenses, they should do so before four pure bhikṣus or bhikṣuṇīs according to the method above; after completing twenty-one days, you should know that they are pure, except if they lack sincerity.