大比丘三千威儀 2.100

2.100

There are ten matters concerning an erection: five involve offense, and five involve no offense. Offense is incurred when: first, it arises from seeing forms; second, it arises from hearing conditions; third, thinking of the beauty of a woman; fourth, thinking of past sensual conditions; fifth, raising it by holding it with the hand—these incur an offense. No offense is incurred when: first, stretching while lying down; second, customary occurrence; third, stretching frequently while lying down; fourth, having a sore on the body and placing the hand near it; fifth, having an urgent urge to urinate and holding it uncontrollably—erection under these circumstances incurs no offense.