四分律行事鈔資持記 2.621

2.621

第二。（佛在舍衛，六群持衣寄親厚，往人間遊行，故制。）名中。三衣簡餘衣，宿者結犯限分。

The second. (When the Buddha was in Śrāvastī, the group of six took their robes and left them with relatives and friends, travelling among people, so it was prohibited.) In the name: "three robes" differentiates them from other robes; "spending the night" sets the limit for determining the offense.