四分律比丘含注戒本 2.223

2.223

佛在舍衛。迦留陀夷與倫蘭難陀尼，俱貌端正，各有欲意，在門外坐。居士共嫌，鴛鴦為喻。比丘聞告，佛因制戒。

The Buddha was in Śrāvastī. Kālodayin and the bhikṣuṇī Sthūlanandā were both handsome in appearance, and each harboured lustful thoughts, sitting together outside the gate. Householders censured them, comparing them to mandarin ducks. The bhikṣus heard this and informed [the Buddha], who instituted the rule on account of it.