四分律刪繁補闕行事鈔 1.55

1.55

謂此宗中，文義俱圓，約事無缺者，當部自足，何假外求？餘有律文不了，事在廢前；有義無文，無文有事；如斯眾例，並取外宗，成此一部。

That is to say, within this school, where both text and meaning are complete and there is no deficiency with regard to affairs, the school's own text is self-sufficient; why rely on external sources? Elsewhere, where the Vinaya text is unclear, where an affair existed prior to an abrogation, where there is meaning but no text, or where there is an affair without a text—in numerous cases like these, one draws from other schools to complete this single school.