四分律行事鈔資持記 1.813

1.813

奴中，初文。《祇律》五種，上三屬主義強，下二則弱，故兩分之。此間投法，多是良人，事亦稀也。

Regarding slaves: In the first passage, the five types in the Mahāsāṃghika-vinaya have the upper three where belonging to a master is strong, and the lower two where it is weak; hence they are divided into two. Here, those who take refuge in the Dharma are mostly freeborn people, so this is also rare.