四分律比丘含注戒本 1.462

1.462

佛在毘舍離。諸梨車子多行邪行，作黑毛氈，披體夜行，使人不見。六群比丘見，便故作之，梨車譏嫌。比丘舉過，佛因制戒。

The Buddha was in Vaiśālī. The Licchavi youths engaged in many perverse deeds, making blankets of black wool and wrapping their bodies in them to walk about at night so that people could not see them. The group of six bhikṣus saw this and deliberately made them as well, which the Licchavis criticized. Bhikṣus raised the fault, and the Buddha laid down the precept on that basis.