Gemara

(Beraisa): The following may only be circumcised in daytime: a Mashuch (his skin is drawn over the crown); a convert who was circumcised before converting; a baby past his time (eight days); and all others who are circumcised, i.e. also one who has two foreskins;

R. Elazar bar Shimon says, in the proper time they are circumcised only during the day. After the time, it may be at night.

The first Tana expounds the Vov in "uva'Yom" (to require Milah during the day even after the time). R. Elazar does not expound the Vov.

(R. Yochanan): Nosar must be burned during the day. After the time, it may be burned even at night.

Question (R. Elazar - Beraisa) Question: ('ba'Yom ha'Shmini' teaches that) Milah on the eighth day must be during the day. What is the source that Milah must be during the day even if it is on day nine, 10, 11 or 12?

Answer: We learn from "uva'Yom".

R. Yochanan: R. Elazar expounds like Moshe learning from Hash-m!

Reish Lakish: R. Elazar learned this from a Beraisa in Toras Kohanim.

Shabbos 137a (Beraisa - R. Chiya): (R. Eliezer and R. Yehoshua argue about one who has two babies to circumcise on consecutive days, and he circumcised the wrong one on Shabbos.) They agree that if on Shabbos he circumcised a nine day old instead of the eight day old, he is liable;

They argue about one who mistakenly circumcised on Shabbos a seven day old instead of the eight day old. R. Eliezer is Mechayev and R. Yehoshua exempts.

Question: If R. Yehoshua exempts in the Seifa, when he did not do a Mitzvah, all the more so he should exempt in the Reisha, when he did a Mitzvah!

Answer (d'Vei R. Yanai): In the Reisha, he circumcised on Erev Shabbos the baby due to be circumcised on Shabbos. On Shabbos he had no Heter to be Docheh Shabbos. In the Seifa, he had a Heter to circumcise on Shabbos.

Megilah 20a (Mishnah): Circumcision is done only after sunrise.

Kidushin 29a - Question: What is the source that women are exempt from Milah?

Answer: We learn from "Like Hash-m commanded him" - not her.

Menachos 72a (Beraisa - Rebbi): If the Omer became Tamei (during the day), if there is more grain available, we harvest it and offer it;

R. Elazar b'Rebbi Shimon says, we offer it b'Tum'ah, for if the Omer was harvested during the day, it is Pasul.

(Rabah bar bar Chanah): R. Elazar b'Rebbi Shimon holds like R. Akiva and like R. Yishmael:

(Mishnah - R. Akiva): Any Melachah (for the sake of circumcision) which can be done before Shabbos does not override Shabbos.

(Mishnah - R. Yishmael): Reaping the Omer is a Mitzvah. It overrides Shabbos.

If an Omer harvested during the day would be Kosher, reaping would not override Shabbos. We would have to reap before Shabbos!

Rishonim

Rif and Rosh (Shabbos 52b and 19:1): A Beraisa learns from "uva'Yom ha'Shmini" that Milah is during the day. This is whether it is on day eight, nine, 10, 11 or 12. It applies to everyone who is circumcised.

Rambam (Hilchos Milah 1:8): We circumcise only during the day after sunrise. This is both in the proper time, i.e. day eight, and afterwards. It says "Ba'Yom" - not at night. If one circumcised after dawn, it is Kosher. The entire day is Kosher.

Kesef Mishneh: R. Yochanan and R. Elazar hold like the Tana who says that Milah is always during the day.

Hagahos Maimoniyos (5): If Milah was done at night, Hatafas Dam Bris must be done during the day. A Mitzvah that must be done at night is invalid if it was done during the day. Likewise, a Mitzvah that must be done by day is invalid if it was done during at night.

Einayim l'Mishpat (Yevamos 72a:20): The Rambam says that Milah is during the day both in the proper time, i.e. day eight, and afterwards. It seems that Milah on day one (e.g. a bought slave) is even at night. However, the Shach says that the Rambam always requires it to be during the day. The text in Toras Kohanim, the Rif and BaHaG says that we circumcise during the day '...and all others who are circumcised not in the proper time.' Our Gemara omits 'not in the proper time', and includes from 'all others' one with two foreskins.

Rosh (19:5): If Milah was done within eight days, Hatafas Dam Bris is not needed. The Gemara says that if one circumcised a seven-day old on Erev Shabbos, he had no Heter to be Docheh Shabbos (for Hatafas Dam Bris). In the Seifa, he had a Heter to circumcise on Shabbos.

Rebuttal (Shach YD 267:2): Hagahos Maimoniyos requires Hatafas Dam Bris if Milah was done at night. The Darchei Moshe says that the Rosh could agree, for Milah before eight days is better than at night. The Gemara in Menachos disproves this. It equates Milah and reaping the Omer, and says that if reaping before the time (Shabbos) would be Kosher, reaping would not override Shabbos! The Rosh's proof is invalid. Really, Hatafas Dam Bris is required, but only Milah itself is Docheh Shabbos.

Rebuttal (of Shach - Sha'agas Aryeh 52): According to this, Milah should never be Docheh Shabbos, because it can be done after eight days! However, a Mishnah (Shabbos 137a) teaches that Milah before eight days is invalid. Milah (of a healthy baby) can be on day eight, nine, 10, 11 or 12. If it is a Safek whether he was during the day or at night, we wait until the (Safek eighth, Safek) ninth day, and if day nine is Shabbos or Yom Tov, we wait until the first Chol day. If Milah was Kosher before eight days, it would be better to circumcise on the (Safek seventh, Safek) eighth day than on (Safek) ninth, for we do not delay Mitzvos. It is surely better than day 10, 11 or 12, which is certainly not the proper time! Also, the Gemara says that one who circumcised on Shabbos a baby on day seven 'did not do a Mitzvah'. The Rosh said that one who circumcised too early need not do Hatafas Dam Bris because there is no Orlah, but he did not do the Mitzvah.

Note: The Rif (54a) says that Hatafas Dam Bris of a baby born circumcised is not Docheh Shabbos, because it is a Safek whether there is covered foreskin. Perhaps he holds that Hatafas Dam Bris is not needed at all when there is no concern for Orlah. However, he could agree with the Rosh and say that Hatafas Dam Bris is Docheh Shabbos when it is definitely needed! Alternatively, the Rosh holds that we could not obligate (for circumcising when there was no Heter to be Docheh Shabbos) if there was a Safek. I.e., perhaps Hatafas Dam Bris should have been Docheh Shabbos (even though the person was not permitted to be Docheh Shabbos due to the Safek).

Maharshal (brought in Mishneh l'Melech Hilchos Melachim 10:7 DH Od Kosav): There is a Mitzvah of Milah fulfilled passively, i.e. not to circumcise before eight days.

Mishneh l'Melech: He should also include the Mitzvah not to circumcise at night! However, the Rosh does not require Hatafas Dam Bris for a baby circumcised within eight days. The Tur (YD 264) learns that the same applies to a baby circumcised at night. This shows that it is only l'Chatchilah not to circumcise at these times.

Poskim

Shulchan Aruch (YD 262:1): We circumcise only after sunrise on the eighth day from birth.

Rema: If one circumcised after dawn, it is Kosher.

Shulchan Aruch (ibid.): The entire day is Kosher for Milah. Even Milah after the proper time is only during the day.

Rema: If Milah was done at night, one must do Hatafas Dam Bris during the day. If one circumcised within eight days during the day, he was Yotzei.

Beis Yosef (DH v'Heicha): The Mishnah connotes that Milah at night is invalid. If so, Hatafas Dam Bris is required. Hagahos Maimoniyos says so. Why did the Poskim omit this? The Rosh does not require Hatafas Dam Bris if Milah was done before eight days; it seems that the Rashba agrees. Regarding other Mitzvos the Mishnah says 'if they were done from dawn (but not before), they are Kosher', but Milah is Kosher b'Di'eved even at night.

Taz (2): The Rema connotes that if Milah was done at night, Hatafas Dam Bris must be done during the day, even on Shabbos. This is wrong. It is a mere stringency; only Hagahos Maimoniyos requires it. Therefore, it is not Docheh Shabbos. Also, within eight days is no better than at night!

Rema (264:1): If there was a need to circumcise a baby before eight days due to danger, it does not matter whether a Yisrael or Nochri circumcises him, for within eight days is not Milah. If strands remain that Me'akev Milah or if Pri'ah was not done, a Yisrael must finish it on day eight.

Source: Rashba, cited in Beis Yosef DH Kosav ha'Rashba.

Gra (10): The Rema contradicts what he said above (264:1). Hatafas Dam Bris is not required, because there is no concern that Orlah remains.

Shulchan Aruch (268:3): L'Chatchilah, all matters of conversion must be in front of three judges and during the day. B'Di'eved, even if he immersed or circumcised in front of two judges or at night, he is a convert and may marry a Yisraelis. However, acceptance of Mitzvos in front of three and during the day is Me'akev. The Rif and Rambam hold that if Milah and Tevilah were in front of two or at night he may not marry a Yisraelis. If he did, we do not disqualify the child.

Rebuttal (Gra 17): The Tur says that the Rif says so, but the Rif did not say so explicitly. The Rambam is Machshir at night b'Di'eved. It seems that the Rif agrees, for he did not ask (why Tevilah Nidah, which is at night, suffices for conversion - 45b). It seems that the Shulchan Aruch meant to cite the Rif and Rambam only regarding two judges.

Beis Yosef (DH u'Mah she'Chosav Ba'al): The Rambam (1:7) says that if a circumcised Nochri converts, he needs Hatafas Dam Bris on the eighth day. This is astounding. We never find Milah of a convert on the eighth day. If he accepts to convert, we circumcise him immediately!

Gilyon Maharsha: Our texts of the Rambam say 'on the day he converts'.