1. The Mishnah Berurah is on the Shulchan Aruch, Orach Chayim 1:3. and the "Se'if Katan" in the Mishnah Berurah is #9. The word "b'Yichud" used by the Mishneh Berurah does not mean that the person referred to is alone, but rather it should translated as "especially."

2. The source of the Mishnah Berurah is the Artzos ha'Chayim, written by the Malbim. (The Mishneh Berurah quotes that Sefer several times in this Halachah, in Sha'ar ha'Tziyun #'s 13, 14, 15.)

3. The Artzos ha'Chayim (at the very end of paragraph 3 in the Shulchan Aruch and in #44) cites two sources for this Halachah. The first is from Pirkei Avos 3:4: "He who stays awake at night... and turns his heart to idle thoughts commits a deadly sin."

4. The second source of the Malbim is from the Gemara in Yoma 19b. The Gemara there states that the honorable people in Yerushalayim would stay awake all through Yom Kippur night. The Gemara then cites a Beraisa that outside Yerushalayim they also did this in memory of the Beis ha'Mikdash, but as a result of staying awake they came to sin.

5. So it appears that even though the Gemara in Yoma 19b also states that one who speaks Sichas Chulin transgreeses a positive commandment, nevertheless this is not the source of the above Mishneh Berurah, but instead the source is a different Gemara, also in Yoma 19b, that says that there are dangers in staying awake all night.

6. Here are further thoughts as to why speaking Sichas Chulin at night is worse than at other times:

a. The first source is the Gemara in Eruvin (18b), where Rebbi Yirmeyah ben Eliezer said that any house where words of Torah are heard at night will not be destroyed. We learn from this the great protection provided by the study of Torah at night.

b. The Tur (Orach Chayim 238) writes that since the night hours are so convenient and desirable for studying Torah, it also follows that if somebody wastes this time his punishment is great.

c. The Rambam (Hilchos Talmud Torah 3:13) explains how important Torah is at night. He writes that one acquires the majority of his learning only at night, and therefore one should not waste a single night "with eating and drinking and talking." In the book "b'Toraso Yehegeh," Rav David Falk (of Ramot, Yerusahalyim) cites the Rambam in the Moreh Nevuchim, the Guide for the Perplexed, that the night hours are blessed with success in learning Torah, so one should not waste a moment of one's waking hours at night (page 260).

d. Rabeinu Yonah, in his commentary on Pirkei Avos 3:4, the Mishnah which states that someone who is awake at night and turns his heart to idle thoughts commits a deadly sin, writes that the reason for this is that at night he does not have work to do, and things are quiet. Therefore, he can think clearly and correctly at night, so if he wastes this time and does not think about Torah, he is held accountable.

Kol Tuv,

Dovid Bloom

Kol Tuv,

Dovid Bloom

(Please forgive the delay in response. Technical problems prevented the mailing of a number of responses.)

Here are further thoughts as to why speaking Sichas Chulin at night is worse than at other times:

1) The first source is the Gemara in Eruvin 18b, where Rebbi Yirmeyah ben Eliezer says that any house where words of Torah are heard at night will not be destroyed. We learn from this the great protection provided by the study of Torah at night.

2) The Tur (Orach Chaim 238) writes that since the night hours are so convenient and desirable for studying Torah, it also follows that if somebody wastes this time, his punishment is great.

3) The Rambam (Hilchos Talmud Torah 3:13) explains how important Torah is at night. He writes that one attains the majority of his Torah learning only at night, and therefore one should not waste a single night with eating and drinking and talking. The Sefer "b'Toraso Yehegeh" (by Rav David Falk of Ramot, Yerusahalyim, page 260) cites the words of the Rambam in Moreh Nevuchim, where he writes that the night hours are blessed with success in learning Torah, so one should not waste a moment of one's waking hours at night.

4) Rabeinu Yonah, in his commentary on Pirkei Avos 3:4 (the Mishnah that says that one who is awake at night and turns his heart to idle thoughts commits a deadly sin) writes that the reason for this is that at night he does not have work to do, and things are quiet. Therefore one can think clearly and correctly at night, so if he wastes this precious time and does not think about Torah, he is held accountable.

5) Another reason for why Sichas Chulin at night is worse than at other times is that nights are long (since one does not have other activities to engage in, such as work), and if one speaks Sichas Chulin he is more prone to get distracted into sinning since the entire night is ahead of him.

Dovid Bloom