釋氏要覽 1.307

1.307

僧祇云。紐緤集要云。前面為鉤。背上名紐。先無此物。因佛制尼師壇。安左臂衣下。則肩上無鎮衣。不整齊。乞食時被風吹落。佛遂許安鉤紐。佛制一切金銀寶物。不得安鉤紐上。惟許牙骨香木之屬。

The Mahāsāṃghika-vinaya mentions 'loop-ties'. The Jiyao says: 'The front has the hook; the back has the loop. Formerly this did not exist. Because the Buddha instituted the niṣīdanamat to be placed under the robe on the left arm, there was nothing weighing down the robe on the shoulder, and it became untidy; when begging for food, it was blown off by the wind, so the Buddha then permitted the addition of hooks and loops. The Buddha instituted that gold, silver, or precious materials must not be used on hooks and loops; only things such as ivory, bone, and fragrant wood are permitted.'