Translation:Shulchan Aruch/Orach Chaim/293

1.  The Laws of the Evening Service on Motzei Shabbat, 3 Seifim: We draw out the Maariv prayer in order to add holiness to the regular week.

2. One must be careful not to do work until he sees three small stars that are not scattered, but rather in a row in one place [in the sky]. If it is a cloudy day, one should wait until he is no longer uncertain at all [that three stars will have appeared].

3. A person who is prevented (from reciting Havdalah), such as one needs to go beyond the techum to perform a mitzvah can pray the prayers for Motzei Shabbos from the time of Plag HaMinchah and may make Havdalah immediately. However, in this case one does not make the blessing over the candle; and it is still forbidden to perform work until the stars come out. ''RAMA: It is our custom to say והוא רחום and ברכו with protracted, melodious tones so as to add from the mundane to the holy. (Or Zarua)''