律戒本疏 1.23

1.23

第二不得離三衣宿　為欲異外道故聽割截衣。為寒故聽三衣。大衣入村。中衣入眾。下衣私處。無功德衣及已捨為離衣。宿後夜時失。後因舍利弗老而衣重。佛聽眾與羯磨留也。凡老而衣重。自咨後無功德衣。九月日中遊行。三衣中墮重者。眾為羯磨捨一無罪也。

Second: One may not spend the night separated from the three robes. In order to distinguish [Buddhists] from non-Buddhists, cutting and piecing robes was permitted. For the cold, three robes were permitted: the saṃghāṭī to enter the village, the uttarāsaṅga to enter the assembly, and the antarvāsaka in private quarters. When there is no kathina robe or it has already been relinquished, spending the night separated from one's robes is lost at the time of the late night. Later, because Śāriputra was elderly and his robes were heavy, the Buddha permitted the assembly to perform a karmavācanā to allow him to leave them behind. In all cases where one is elderly and robes are heavy, after the pravāraṇā, when there is no kathina robe and one travels during the nine months, if any of the three robes is burdensome, the assembly performs a karmavācanā to relinquish one without offense.