梵網經菩薩戒本疏 4.26

4.26

第二、釋名者，勝德可珍，故稱「三寶」；非理塵黷，故名為「謗」；戒防此失，故以為名。

Second, explaining the name: superior virtue is worthy of cherishing, hence it is called the "Three Jewels"; defiling them contrary to reason, hence it is called "slander"; the precept prevents this fault, hence it is used as the name.