四分律比丘含注戒本 2.41

2.41

若共二宿，若三宿，明相未出，應起避去。至第四宿，若自去，若使未受者去。

If staying together for two nights or three nights, before the first light of dawn appears, one should get up and leave. When it comes to the fourth night, either leave oneself or have the unordained person leave.