四分律比丘含注戒本 2.11

2.11

佛在舍衛。六群於斷事人前種類罵，彼忘失前後，慚愧不語。比丘以過白佛。便引牯牛以譬，「畜生得毀，不堪進力」等，便制此戒。

The Buddha was in Śrāvastī. The group of six [monks] reviled the arbiter of disputes according to his class, so that he became confused about what came before and after and fell silent in shame. The bhikṣus reported the fault to the Buddha. [The Buddha] then drew the simile of a bull: "Even a beast, when reviled, cannot exert its strength," and so forth, whereupon he laid down this precept.