四分律刪補隨機羯磨 2.184

2.184

(At one time, a bhikṣu went to another place for the retreat: when one foot entered the garden or the boundary, dawn broke; in another case, when both feet entered the garden or the boundary, dawn broke; in another case, having entered the garden or boundary with both feet, dawn had already passed. The Buddha said: "All of these effect the retreat." According to common understanding, the latter two procedures apply to the sixteenth day of either the earlier or later periods. If it is the intermediate retreat, it may be bound on any appropriate day.)