四分律刪繁補闕行事鈔 2.305

2.305

三反抄衣者。謂左右反抄，著肩上也。若脇有病，在寺中道行作時者得。

Third, the precept against throwing the robe backwards over the shoulders. It means folding it backwards on the left and right and placing it over the shoulders. If one has an ailment on the ribs, or when walking the path or working in the monastery, it is permissible.