Can one rinse out the kiddush cup on Shabbos to prepare for the mitzvah of havdalah, or this is considered preparing for the weekday which is forbidden?
Answer:
If it is clear that the kiddush cup won't be used until after Shabbos, it should not be rinsed on Shabbos.
Sources: Mishnah Berurah (323:29, based on Magen Avraham) writes that this would be "forbidden," whereas Aruch Hashulchan (323:7) writes that it is "improper."
