四分律比丘含注戒本 2.788

2.788

佛在舍衛。諸佛常法，若不受請，遍行房舍，見僧臥具敷在露地，不淨污之，告諸比丘：「外道仙人離欲者尚無此事。聽為障衣、障臥具故，作尼師壇。」六群大作，比丘舉過，佛因制戒。

The Buddha was in Śrāvastī. It is the regular practice of the Buddhas, when not accepting an invitation, to inspect the dwellings everywhere. Seeing the bedding of the saṃgha spread on the open ground and soiled with impurities, he told the bhikṣus: "Even non-Buddhist seers who have abandoned desire do not do this. I permit you to make a niṣīdāna to protect your robes and protect your bedding." The Group of Six made them oversized; the bhikṣus reported the fault, and the Buddha accordingly formulated the precept.