When a Berit Mila is performed on Shabbat, it is often performed in the synagogue immediately after the prayer service. Several Halachic authorities note – and the Ben Ish Hai records that this was the practice in Baghdad – that the Beracha recited over a cup of wine at the Berit fulfills the obligation of Kiddush. The one who recites the Beracha should have in mind to fulfill the Misva of Kiddush, and should then drink a Rebi’it (approximately 3.2 ounces) in order to fulfill the requirement to recite Kiddush in the context of a "meal." Everyone else, however, does not fulfill the obligation of Kiddush unless they eat a Ke’zayit of bread or "Mezonot" food. If only fruit is served, they may not partake of the fruit, as this does not suffice to fulfill the Kiddush obligation, and eating is forbidden on Shabbat until one fulfills the Kiddush obligation. (The Mishna Berura notes that one who is ill may eat, if necessary, before hearing Kiddush, but as a general rule, one may not eat or drink before Kiddush on Shabbat.)
If one recites Kiddush in one corner of a room, even in a very large room, he may eat his meal in the other corner of the same room. For example, if a person attends a "Sebet" on Shabbat in a large banquet hall, he may recite Kiddush in one end of the room and then eat somewhere else in the room. He should have in mind when he recites Kiddush that he will eat in a different part of the room, though even if he did not have this intention when he recited Kiddush, he is nevertheless allowed, after the fact, to then eat somewhere else in the room.
The Poskim address the interesting case of somebody who is unable to recite Kiddush, and asks his neighbor – for example, the person who lives in the apartment right across the hall – to recite Kiddush on his behalf. The person remains at home, sitting by his table, and listens to his neighbor across the hall reciting Kiddush. The Shulhan Aruch writes that in such a case, the person fulfills his obligation of Kiddush, because one who hears Kiddush is considered as though he recites it. Therefore, since he hears Kiddush in the place where he will then eat his meal, he fulfills the obligation. He may not, however, go across the hall to his neighbor’s apartment for Kiddush and then return to his apartment for his meal. In this case, the Kiddush and the meal are occurring in two different locations, and thus the obligation is not fulfilled.
Summary: When a Berit Mila is held in the synagogue on Shabbat immediately after the prayer service, the one who recites the Beracha over wine should have in mind to fulfill his obligation of Kiddush with this recitation, and then drink a Rebi’it of wine. Everyone else fulfills their obligation of Kiddush only if they then eat a Ke’zayit of bread or of "Mezonot" food. One who attends a "Sebet" in a large hall may recite Kiddush in one part of the room and then eat in a different part of the room. One who asks his neighbor to recite Kiddush for him while he remains in his home fulfills the Misva of the Kiddush, even though the neighbor is in a different home.
