大方便佛報恩經 6.71

6.71

“These two classes of precepts are the gravest. If one violates one precept [of the former], it will never arise a second time. Even if it could arise, it is difficult to restore: through parivāsa and mānatva, one is purified of the offense only within an assembly of twenty monks. If one is able to uphold what is difficult to uphold, the remaining classes of precepts are easy to uphold and need not be mentioned; therefore only the two classes are spoken of, and the remaining classes are not spoken of.”