四分律比丘含注戒本 1.299

1.299

佛在舍衛國。迦留陀夷先俗友婦齋優婆私，形並端正，各有繫意。時到詣彼，共屏覆坐，說非法語。毘舍佉母闚見起過，疾往白佛，因訶制戒。

The Buddha was in the country of Śrāvastī. An upāsikā who observed the eight precepts was the former wife of a lay friend of Kālodayin; both were handsome in appearance and felt mutual attachment. When the time arrived, he went there and sat together with her in a secluded and covered place, speaking unlawful words. The mother of Viśākhā peeked and saw this transgression arise, and hurried to report it to the Buddha. Because of this, [the Buddha] rebuked him and formulated the precept.