四部律并論要用抄 2.55

2.55

殘宿食戒　四分云。今日受食至明日。於一切沙門釋子皆不清淨　僧祇云。停過一須臾犯。須臾者二十念名一瞬。頃一彈指一羅預名須臾。日極長時盡有十八須臾頃。夜有十三須臾。夜長短亦如是。若過一須臾即名為犯。

The precept on remaining food kept overnight: The Caturvargika-vinaya states: Food received today kept until tomorrow is impure for all śramaṇas, sons of the Śākya. The Mahāsāṃghika-vinaya states: If it is kept for more than one muhūrta, it is an offense. As for a muhūrta, twenty kṣaṇas are called one twinkling of an eye; the snap of a finger is one lava, and [thirty lavas] are called a muhūrta. When the day is at its longest, it lasts for eighteen muhūrtas; the night has twelve muhūrtas. The length and shortness of the night are also like this. If it exceeds one muhūrta, it is an offense.