四分比丘戒本疏 2.53

2.53

第二十一，准律，令尼半月半月請教誡人，若有具足十德比丘受尼請。時，僧須白二差教授尼。今不被差輒往教尼，犯提也。此義如上戒序中已略述之。

Twenty-first: according to the vinaya, the bhikṣuṇīs are to request an instructor every half-month; if there is a monk endowed with the ten virtues who receives the bhikṣuṇīs' request, the saṃgha must perform a ñattidutiya-kamma to appoint him to instruct the bhikṣuṇīs. Now, if one goes on one's own initiative to instruct the bhikṣuṇīs without having been appointed, one incurs a prāyaścittika. This meaning has already been briefly explained above in the preface to the precepts.