Hilchos Sukkos 3 - When it Rains on the First Night of Sukkos

(7) 7. If one is sleeping and it begins to rain at night, and one enters his house and the rain then stops, we do not bother him to return to the sukkah for the rest of that night. Rather, he should sleep in his house until dawn. RAMA: and then he wakes from his sleep (Tur). One who sleeps in the sukkah and it starts to rain does not have to wait the time that it takes for the dish to spoil, because even sleeping in light rain is unpleasant and he is allowed to leave. [Mahari"v] Whenever one is exempt from [the mitzvah] of sukkah, but does not leave the sukkah, he is not rewarded for dwelling there [at that time]. Instead, he is considered a commoner [Hagahos Maimoni]. When one leaves the sukkah because of rain, he should not leave brazenly, but submissively, like a servant who came to pour a drink for his master, and his master poured it out on his face, (as if to say, “I do not desire your service). (Mahari"l).

(3) Eating in the Sukkah on the first night, is obligatory. If he ate an olive sized amount of bread, he has fulfilled his obligation. Henceforth it is optional; if he wished to eat a meal, he eats in the Sukkah; if he wishes, he can eat only fruits and nuts outside of the Sukkah all seven days, like the rules of eating Matzah on Pesach. Rem"a: And he should not eat on the first night until it is certainly night (Bet Yosef in the name of the Orchot Chayyim), and he should eat before midnight (Mahar"i Weill and Mahari"l); and he should not eat during the day from noon and onwards, so that he will eat in the Sukkah hungrily (Mahari"l), similar to eating Matzah.

(4) 4. One who is discomforted is exempt from the Sukkah, he, and not his attendants. But on the first night even the discomforted one must eat an olive-portion there (Kol Bo). Who is discomforted? He who cannot sleep in the Sukkah because of the wind; or because of the flies, fleas, and their ilk; or because of the smell. But this is only when the discomfort occurred by chance, after he built the Sukkah there, but he shouldn't build his Sukkah a priori in a smelly or windy place, and say, "I am discomforted ". Rem"a: And if he built it, at the beginning, in a place where he is discomforted while eating, or drinking, or sleeping, or he cannot do one of them in the Sukkah since he fears bandits or thieves while he is in the Sukkah, he does not fulfill his obligation in the Sukkah at all, even in the activities in which he is not discomforted , for it is not like a dwelling which one can do all his functions within (Mordekhai, chapter 'HaYashen'). He whose candles in the Sukkah were extinguished, on the Sabbath, and has a candle in his house, it is permitted for him to leave the Sukkah to eat where the candle is, and he does not need to go to his friend's Sukkah which has a candle, if there is great effort involved (Terumat HaDeshen, Part I 5, Terumat HaDeshen, Part II 158). And if the wind is threatening to extinguish the candle, it is permitted to hang a sheet or garment from the side, but not under the skhakh (Or Zarua). He who cannot sleep in the Sukkah, because it is too small for him to extend his hands and legs, is not considered discomforted, and must sleep there, even though he needs to curl up (Terumat HaDeshen, Part I 92), and he cannot say: "I am discomforted", unless it is something from which it is normal for one to be discomforted (Tur). And the discomforted is not exempt unless he will save himself from the discomfort, but otherwise, he must sleep in the Sukkah, even if he is discomforted (Mordekhai, chapter 'HaYashen').

(5) 5. If it rains, one may go inside his house. From when is it permitted to go inside? From when so many drops of rain descend into the sukkah that, were they to fall into a cooked dish of beans which spoils quickly if only a small amount of water is added to it, that dish would spoil. RAMA: Even if he does not have a dish in front of him [Sma"g and Hagahos Ashiri]. A person who does not know how to calculate such a measure should reckon: If this same quantity of rain would come down into his house, he would leave his house, he may leave the sukkah. [Hagahos Ashiri; Mordechai; Mahari"l]. All of this applies specifically to the remaining days of the festival of Sukkot. But on the first night, one must eat an olive's worth in the sukkah even if it is raining [Tur; R"an; Rosh] and one must say Kiddush in the sukkah so he can pronounce the Zman regarding the sukkah

(7) 7. If one is sleeping and it begins to rain at night, and one enters his house and the rain then stops, we do not bother him to return to the sukkah for the rest of that night. Rather, he should sleep in his house until dawn. RAMA: and then he wakes from his sleep (Tur). One who sleeps in the sukkah and it starts to rain does not have to wait the time that it takes for the dish to spoil, because even sleeping in light rain is unpleasant and he is allowed to leave. [Mahari"v] Whenever one is exempt from [the mitzvah] of sukkah, but does not leave the sukkah, he is not rewarded for dwelling there [at that time]. Instead, he is considered a commoner [Hagahos Maimoni]. When one leaves the sukkah because of rain, he should not leave brazenly, but submissively, like a servant who came to pour a drink for his master, and his master poured it out on his face, (as if to say, “I do not desire your service). (Mahari"l).