俱舍論記 18.5

18.5

「論曰至不可害故」者，五無間中四是身業，謂殺父、害母、殺阿羅漢、出佛身血；一是語業，謂破僧。三是殺生根本業道，謂殺父、害母、殺阿羅漢；一虛誑語根本業道，謂破僧；一是殺生業道加行，謂出佛身血，以如來身不可害故。

Regarding "The commentary says: ... because it cannot be killed": among the five uninterrupted [offenses], four are bodily karma—namely, killing the father, slaying the mother, killing an arhat, and shedding the blood of a Buddha's body; one is vocal karma—namely, causing a schism in the Saṃgha. Three are fundamental courses of action of killing—namely, killing the father, slaying the mother, and killing an arhat; one is a fundamental course of action of false speech—namely, causing a schism in the Saṃgha; one is a preparatory application of the course of action of killing—namely, shedding the blood of a Buddha's body, because the Tathāgata's body cannot be killed.