大比丘三千威儀 1.79

1.79

問經有五事：一者當如法下床問；二者不得共坐問；三者有不解直當問；四者不得持意念外因緣；五者設解，頭面著地作禮反向出戶。

There are five matters regarding asking about the sūtras: first, one must step down from the bed according to the Dharma to ask; second, one must not sit together to ask; third, if there is something one does not understand, one should ask directly; fourth, one must not let the mind dwell on external circumstances; fifth, if one understands, one must touch head and face to the ground in homage, and exit through the doorway facing backward.