大比丘三千威儀 2.37

2.37

若著僧伽梨時，持手巾有五事：一者不得使巾頭垂見；二者不得持白巾；三者當敗色令黑；四者不得拭面；五者飯當用覆膝上，飯已當下去。設不去，若有來作禮、若起去，先取襞去之。

When wearing the saṃghāṭī, carrying the hand-cloth has five matters: first, one must not let the ends of the cloth hang down and be visible; second, one must not carry a white cloth; third, one should ruin its color to make it dark; fourth, one must not wipe the face; fifth, when dining, one should use it to cover the knees, and when dining is finished, remove it. If it is not removed, whenever someone comes to pay respects or when one stands up to leave, first take and fold it away.