On the afternoon of Shmini Atzeret, it is customary to visit the Sukkah for one last time to “take leave” of the Sukkah. In Yiddish, this is referred to as "bazegennen zich mit di Sukkah,” saying good-bye to the Sukkah.
There is a Yehi Ratzon prayer that many recite on this occasion. In it one prays that we should merit to sit in the Sukkah made of the Leviathan skin. The Chabad custom is to not recite this but to have a little snack in the Sukkah.
The prayer (that some say) is:
יהי רצון מלפניך ה׳ אלוקינו ואלוקי אבותינו, כשם שקיימתי וישבתי בסוכה זו, כן אזכה לשנה הבאה לשבת בסוכת עורו של לויתן .
“May it be Your will, Hashem, our G-d and the G-d of our fathers: just as I fulfilled the mitzvah and sat in this Sukkah, so may I merit next year to sit in the Sukkah of the Leviathan's skin.”
In Israel, one should take leave of the Sukkah in the afternoon of Hoshana Rabbah.
