Although it is generally forbidden to eat or drink after sundown on Shabbat afternoon until Habdala, one who began eating Se’uda Shelishit before sundown may continue his meal after sundown; he may eat and drink until ending the meal with the recitation of Birkat Ha’mazon.
Many people have the custom of reciting Birkat Ha’mazon over a cup of wine, which is drunk after Birkat Ha’mazon. The question arises as to whether one who recites Birkat Ha’mazon over a cup of wine after Se’uda Shelishit is permitted to then drink the wine if Birkat Ha’mazon is recited after sundown. On the one hand, Halacha allows eating and drinking after sundown only as part of Se’uda Shelishit, and once one recites Birkat Ha’mazon, the Se’uda 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’uda 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’mazon unless he customarily recites Birkat Ha’mazon over a cup of wine and then drinks it afterward. Otherwise, if this is not one’s ordinary practice, then he may not drink the wine after Se’uda 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’mazon over a cup of wine. Even if one recites Birkat Ha’mazon 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’mazon after Se’uda 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’mazon at other times. Regardless, the common custom follows Hacham Ovadia’s ruling, that in all circumstances, one may drink the cup of wine over which he recited Birkat Ha’mazon after Se’uda Shelishit, even if Birkat Ha’mazon is recited well after sundown.
Summary: If one ends Se’uda Shelishit after sundown at the end of Shabbat, he may not eat or drink after Birkat Ha’mazon until Habdala, but he is allowed to drink the cup of wine over which he recited Birkat Ha’mazon.
