四分律行事鈔資持記 2.471

2.471

第一戒。（佛在舍衛，迦留陀夷欲盛身瘦，便念棄失，諸根悅豫，佛訶制戒。）標名。言故者，對下開通不作意也。

The first precept. (The Buddha was in Śrāvastī; Udāyin's sexual desire was intense and his body became emaciated, so he thought of discharging [semen], and his sense faculties became joyful; the Buddha rebuked him and instituted the precept.) Indicating the title. Saying 'intentional' contrasts with the exception below for lack of deliberate intention.