四分律比丘含注戒本 2.35

2.35

The Buddha was in the city of Aṭavī. The group of six [bhikṣus] lodged together with householders in a lecture hall; at night they slept with disturbed minds and exposed bodies, and were mocked by them. They reported it to the Buddha, who thereupon formulated [the rule]. When the Buddha was in Kauśāmbī, he then permitted two or three nights, and reformulated this precept.