俱舍論疏 9.243

9.243

論「禁謂狗牛等禁」者，是外道持狗、牛等禁。此不能離惡戒，故不名戒。

As for the treatise stating: "'Observances' refers to the observances [mimicking] dogs, oxen, and so on," these are the observances maintained by non-Buddhists [mimicking] dogs, oxen, and the like. Because these cannot abstain from bad precepts, they are not called rules.