四分律比丘含注戒本 3.96

3.96

The Buddha was in Śrāvastī. A householder invited the Saṃgha to his home to offer a meal. The group of six squatted, and being jostled by their seat-mates, they fell backward, exposing themselves. The householders disparaged them, saying: "Shameless! Exposing themselves just like brahmins." The bhikṣus reported the fault, and the Buddha thereupon reproached them and laid down the precept.