Although it is generally forbidden to eat or drink after sundown on Shabbat afternoon until Habdala, one who began eating Se置da Shelishit before sundown may continue his meal after sundown; he may eat and drink until ending the meal with the recitation of Birkat Ha知azon.
Many people have the custom of reciting Birkat Ha知azon over a cup of wine, which is drunk after Birkat Ha知azon. The question arises as to whether one who recites Birkat Ha知azon over a cup of wine after Se置da Shelishit is permitted to then drink the wine if Birkat Ha知azon is recited after sundown. On the one hand, Halacha allows eating and drinking after sundown only as part of Se置da Shelishit, and once one recites Birkat Ha知azon, the Se置da Shelishit meal has concluded, and drinking then becomes forbidden. On the other hand, one might argue that since this cup of wine is closely associated with Se置da Shelishit, it may be drunk, even though it is already after sundown.
This issue is subject to a debate among the Halachic authorities. The Magen Abraham (Rav Abraham Gombiner, Poland, 1635-1782) maintains that one may not drink the wine after Birkat Ha知azon unless he customarily recites Birkat Ha知azon over a cup of wine and then drinks it afterward. Otherwise, if this is not one痴 ordinary practice, then he may not drink the wine after Se置da Shelishit if the sun had already set. Hacham Ovadia Yosef, however, in Yabia Omer, rules that one may drink the wine in this case even if he does not normally recite Birkat Ha知azon over a cup of wine. Even if one recites Birkat Ha知azon well after dark at the end of Shabbat, he may nevertheless drink the cup of wine. This is also the position taken by the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), who claims that even according to the Magen Abraham, one who regularly recites Birkat Ha知azon after Se置da Shelishit over a cup of wine may drink the wine after sunset, even if he does not normally use a cup of wine for Birkat Ha知azon at other times. Regardless, the common custom follows Hacham Ovadia痴 ruling, that in all circumstances, one may drink the cup of wine over which he recited Birkat Ha知azon after Se置da Shelishit, even if Birkat Ha知azon is recited well after sundown.
Summary: If one ends Se置da Shelishit after sundown at the end of Shabbat, he may not eat or drink after Birkat Ha知azon until Habdala, but he is allowed to drink the cup of wine over which he recited Birkat Ha知azon.
