Hilchot Shabbat 29:28-29 (The reason for the spices during Havdalah)
10:40 pm
Why, after Yom Tov, do we use the same text for Havdalah as we do after Shabbat, mentioning the distinction “between the seventh day and the six days of activity”? What is the reason that we have a blessing over spices when Shabbat is over?