For the source text click/tap here: Chullin 26
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Our final Mishnah teaches that when the sound of the shofar on Shabbat or a Festival evening stop people from working and mark a line between the sacred and the profane, there is no havdala at the conclusion in prayer over wine. When havdala is recited, there is no shofar.
How is this the case? When a Festival falls on erev Shabbat, the shofar is sounded to stop people from working at tasks prohibited on Shabbat but permitted on the Festival. Havdala is only performed when the transition from a sacred to a profane day or from a day of greater to lesser sanctity. Shabbat is more holy than a Festival.
When havdala marks the transition between a Festival and Shabbat, it ends with the following words, "Who distinguishes between sacred and sacred" instead of the standard blessing, "Who distinguishes between sacred and profane". Rabbi Dosa says that we should say,"Who distinguishes between greater sanctity and lesser sanctity.”