A. What is Nittel?
Nittel is a gentile Holiday celebrating the birth of Yoshke. On this day there is an extra abundance of impurity and a stronghold of Kelipa. For this reason, the Jews throughout the generations took various customs upon themselves which are followed until this day, in order to diminish the spiritual power of the impurity. The word Nittel is at times spelled with a “Tes” and at times with a “Taf” . The meaning of Nittel with a Tes is “removed”, as on this night there is a lack of Kedusha. The word Nittel with a “Taf” means “Natleh” which means birth in Latin.
B. When is Nittel?
Nittel is on the 25th of December. The customs of Nittel apply starting from the night before the 25th, which is on the night of the Eve of the 25th of December.
C. Avoiding learning Torah:
It is the custom of many Jewish communities, dating back several generations, to avoid learning Torah on the night of Nittel. This is likewise the Chabad custom. This applies even in Eretz Yisrael. The Rebbe Rashab was not keen with those students who ignored this custom and continued with their studies as usual. The reason that Torah learning is avoided, is because we do not want to add vitality to the impure spirit that exists on this day. Other reasons are also recorded. It is told of a certain Gadol Beyisrael who learned on this night, and his learning attracted a dog to the home, hence symbolizing the nurture of Kelipa from one’s Torah learning.
D. When is one to avoid learning on Nittel?
The custom to avoid learning begins from the night of the Eve of the 25th of December [as explained above]. One is to avoid learning Torah until midnight. Starting from midnight, one may resume learning Torah, and there are no longer any restrictions applicable.
When is midnight? Midnight in this regard is in accordance to Halachic Zmaniyos hours, and is not exactly at 12:00, when the date changes.
May one learn Chassidus on Nittel?
One is to avoid learning even Chassidus on the night of Nittel. This applies even when the night of Nittel falls on Shabbos.
May one read stories of Tzaddikim on Nittel?
May an Avel learn Mishnayos to recite after Maariv?
How should one use his time during Nittel?
The time of Nittel is to be used wisely, and not to be wasted G-d forbid. One is to use his time to perform matters which involve wisdom and sharpen the mind, or to perform Chesed, or matters dealing with the home. The Rebbe suggested the following activities as examples of how one can use his time on the night of Nittel.
1. Play chess. The Rebbe Rashab was accustomed to play chess on this night, or to advise other players in the midst of their game.
2. Sew buttons of his coat right over left.
3. Look at pictures of Rabbeim
Story with the Tzemach Tzedek:
One year, the Rav of Lubavitch entered the study of the Tzemach Tzedek on the night of Nittel and found the Tzemach Tzedek engrossed in learning. The Rav exclaimed in shock “Rebbe, tonight is Nittel”. The Tzemach Tzedek responded “Who asked you to inform me?” Nonetheless, the Rebbe proceeded to close his Sefer and ceased his learning.
E. May one have marital relations on Nittel Nacht?
Some Poskim rule one is to avoid marital relations on the night of Nittel. This applies even on the night of Mikveh. However, after midnight, one may be lenient on the night of Mikveh. Others however rule that those who are lenient have upon whom to rely, while those that are stringent are blessed.
 Sefer Haminhagim Tirana 14; Kaftor Vaferach 10; Levush 148; Igros Kodesh 13:120; 14:352; Likkutei Sichos 15:545
 Machzor Vitri Shechita 80; Terumos Hadeshen 195; Darkei Moshe Yoreh Deah 148; Hayom Yom 17th Teves; Sefer Hasichos 1990 1:192; Reshimos Hayoman p. 313, 365
 Likkutei Sichos 15:545
 In the secular calendar the date begins at midnight. Nevertheless, the customs of Nittel are guarded on the night of which the 25th will begin at midnight.
 See Darkei Chaim Veshalom 828; Nitei Gavriel Nittel
 Chasam Sofer 7:31; Makor Chaim of Chavos Yair 155; So was the custom of many Jewish communities including: Rav Yonason Eibashitz, Rav Yaakov Emden that so is custom of all Geonim, Rav Yisrael Salanter, Maharsha, Maharam Schick and others. See Nitei Gavriel Chanukah p. 385
 Hayom Yom 17th Teves
 So is the custom; However, see Igros Kodesh 13:120
 Hayom Yom ibid
 Likkutei Sichos 14:554; Igros Kodesh 13:120; 14:351; Reshimos Hayoman p. 365 [printed in Shaareiy Halacha Uminhag p. 179]
 Other reasons: As in previous times, the night of their festival was a time of danger for Jews to be out in public, and therefore they decreed that Jews should not go to the Beis Hamidrash on this night. [Likkutei Sichos 15:554]
 Darkei Chaim Veshalom 825
 Hayom Yom 17th Teves; Hisvadyus 5750 2 p. 49; Reshimos Hayoman p. 365, printed in Shaareiy Halacha Uminhag p. 179
 Nitei Gavriel Luach Dvar Beito
 Hiskashrus footnote 14
 Reshimos Hayoman p. 365 that the Rebbe Rashab did not learn Chassidus on the night of Nittel, not even in a form of Girsa. [printed in Shaareiy Halacha Uminhag p. 179]; Directive of Rebbe to Rav Weinberg who gave a radio class in Tanya; Even when Nittel fell on Shabbos, the Rebbe Rashab did not say the Mamar at night but rather on Shabbos day. [Reshimos Hayoman ibid]
Other opinions: In Reshimos Hayoman p. 313 it states that the learning of Chassidus is not relevant to the custom of avoiding learning on Nittel.
 Directive of Rebbe to Rav Weinberg who gave a radio class in Tanya.
 Hisvadyus 5750 Vol. 2 p. 50 [Sichas Vayeishev, Chanukah 5750]
 This is done as a) It adds sharpness to the mind, which allows one to learn Torah with greater understanding in the future. [See Kesubos 61b in Rashi “Demitlala”] B) It sanctifies Hashem’s name and the praise of the Jewish people by showing the gentiles that the Jews are also wise even in this wisdom. C) Some play this game for business, and it hence is no different than any other business. [Rebbe ibid]
 See Nitei Gavriel Chanukah p. 410; Beir Moshe 4:69; Piskeiy Teshuvos 240:10; Shulchan Menachem 6:242; Taharah Kehalacha 21
 Taharas Yisrael 197:2-3; Karban Nisanel; Yimtza Chaim 73:9; See Nitei Gavriel Chanukah p. 410; Beir Moshe 4:69
 The reason: As many Poshei Yisrael were born from mothers who conceived on this night. [See Nitei Gavriel ibid] Alternatively, this is because marital relations requires purity of mind, and the thinking of Nittel, even negatively, can affect the born child, and due to this worry they forbade marital relations on this night. [Rebbe in Shaareiy Halacha Uminhag 4:132; Shulchan Menachem 6:242; Igros Kodesh 4:424]
 Taharas Yisrael 197:2-3; Darkei Chaim Veshalom 825; See Shaareiy Halacha Uminhag 4:132; Beir Moshe ibid that so was custom of students of Baal Shem Tov
 Darkei Chaim Veshalom ibid; Shiureiy Shevet Halevi 197:2; Taharah Kehalacha 21:9; See Shulchan Menachem ibid;
On a regular night: The Munkatcher rules one is to avoid marital relations even after midnight. [See letter of Rebbe ibid] So is also implied from Taharas Yisrael ibid, and other Poskim. [Piskeiy Teshuvos ibid]
 Beir Moshe 4:69; Chasam Sofer Koveitz Hateshuvos 31 protested the custom of closing the Mikvas on this night
 As there is no source in Poskim to prohibit it. [ibid]