釋氏要覽 2.41

2.41

天竺之儀也。此禮自曹魏世寢至今也。律云偏露右肩。即肉袒也。律云。一切供養。皆偏袒。示有便於執作也。亦如仲尼云。矩右袂便作事也（言一切供養即見佛禮佛及禮二師等）若入聚落俗舍。皆以袈裟通披之。

This is an etiquette of Tianzhu. This rite has lapsed since the Cao-Wei period down to the present. The Vinaya says that baring the right shoulder means baring the flesh. The Vinaya says: For all offerings, one bares one shoulder, showing readiness to perform manual work. It is also as Zhongni (Confucius) said: Gathering up the right sleeve facilitates doing work. (Saying 'all offerings' refers to seeing the Buddha, paying homage to the Buddha, paying homage to the two masters, and so forth.) If entering villages or lay dwellings, one covers both shoulders with the kāṣāya.