四分律行事鈔資持記 3.87

3.87

In the seventh [part], it cites a sūtra to show the intent behind baring one shoulder versus covering both shoulders. In the Vinaya, only when the Buddha or senior monks were in front did one bare the shoulder; from this it can be verified that at other times it was draped over both shoulders. In the sūtra text, it is not clear which sūtra it is; it means that doing otherwise shows a lack of respect before the Buddha and Saṅgha.