Translation:Shulchan Aruch/Orach Chaim/291
291: The Law of Three Meals. Contains 6 seifim.
1 One should be very cautious to fulfill the third meal. And even if he is sated, he could fulfill it with about the volume of an egg. And if he cannot eat at all, he is not obligated to cause himself sorrow. And the wise person – his eyes are in his head that he shall not fill his stomach with the morning meal, so as to give room for a third meal. Gloss: And one who did not eat on the night of Shabbat should eat three meals on the day of Shabbat. (The Rosh, Chapter "Eves of Pesahim").
2 Its time: From when the time of minchah will arrive, which is from six and a half hours and onward. And if one did it earlier, he has not fulfilled the mitzvah of the third meal. Gloss: There are those who say that it is prohibited to drink water between minhah and maariv on Shabbat for then the souls return to Gehinom. And therefore, one should not eat the third meal between minhah and maariv. Instead, he should eat it before minhah (Tosafot and the Rosh and Mordecai, Chapter "Eves of Pesahim"). And there are those who say that it is preferable to pray minhah first (Rambam; and Tur; and Hagahot Mordecai; and Hagahot Maimoni, Chapter 30; and Agur). And this is our preferred custom in all of these lands. In any case, one should not drink water from the rivers, but it is permissible in the house. And all the more so, other liquids, that they are permissible (Hagahot Maimoni, Chapter 30). And there are those who say that it is prohibited only during the 12 months of one's father and mother (Agudah and Mordecai, Chapter "Eves of Pesahim"). And there are those who say that this prohibition of drinking water is only on the Eve of Shabbat (Tosafot; and the Rosh; and Mordecai in the name of Rabbi Meshulam; and Hagahot Maimoni).
3 If the morning meal was extended until the time of the minchah arrives, one should stop the meal, and should recite birkat hamazon, and should wash one's hands, and should recite the blessing of hamotzi, and should eat the meal. And the matter is correct, for if one would not do so, since the morning meal was extended until that time, he would not be able to eat afterwards except by overeating.
Gloss: However, one who knows that he is able to eat after reciting minchah prayer with the congregation, should not perform the third meal before minchah. But if he did it, he has fulfilled the obligation.
4 One does not need to recite kiddush during the third meal, but one needs to break bread over two loaves. Gloss: And if one partakes of many meals on Shabbos, he needs two loaves for every meal (Avudraham and Maimoni). And at least, he should not have for the third meal less than 1 complete loaf [Tur; and Mordechai, Chapter "All Writings"]. And from this, the custom has become widespread to be lenient to break bread for the third meal on one whole loaf alone. But there is what to be stringent in, to take two.
5 One needs to perform it with bread. And there are those who say that one could perform it with whatever food is made with one of the five types of grain. And there are those who say that one could perform it with things that go with the bread – with meat and fish, but not with fruits. And there are those who say that one could perform it even with fruits. And the first opinion is the essence, that one needs to perform it with bread, unless he is severely full. Gloss: Or in a place where it is impossible for one to eat bread, like on Erev Pesach that falls on Shabbat, when it is forbidden for him to eat bread after minchah, as brought below in the laws of Pesach. [Mahari"l, Laws of Pesach].
6 Women are obligated in the third meal.