四分律比丘含注戒本 2.11

2.11

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.