四分律比丘含注戒本 2.674

2.674

佛在舍衛。六群中一人當說戒時，自知罪障，恐發舉故，先詣清淨比丘所言：「我今始知此法《戒經》所載，半月半月說，《戒經》中來。」比丘舉過，佛制此戒。

The Buddha was in Śrāvastī. When it was time to recite the precepts, one among the group-of-six, knowing himself to have an obstructive offense and fearing that someone would bring an accusation, went first to a pure bhikṣu and said: "Only now do I know that this rule is contained in the Prātimokṣa Sūtra, recited half-month by half-month, and comes from within the Prātimokṣa Sūtra." The bhikṣus reported his fault, and the Buddha instituted this rule.