(Mishnah) Question: From (and until) when do we recite Keri'as Shma at night?

Answer #1 (R. Eliezer): The Mitzvah is from the time when Kohanim enter to eat their Terumah, until the end of the first Mishmar (these will be explained).

Answer #2 (Chachamim): It is until midnight.

Answer #3 (R. Gamliel): It is until dawn.

A case occurred in which R. Gamliel's sons came home from a wedding after midnight. They told him, we did not recite Shma.

R. Gamliel: If dawn did not come, you are obligated to recite [it now];

Not only this (is until dawn). Rather, wherever Chachamim said "until midnight,'' the (Torah) Mitzvah is until dawn:

Burning [on the Mizbe'ach] Chelev (of Korbanos) and limbs (of an Olah), their Mitzvah is until dawn;

All Korbanos that may be eaten for one day [and a night], their Mitzvah is until dawn.

Question: If so, why did Chachamim say "until midnight''?

Answer: This is to distance people from transgression (lest dawn arrive before one performs the Mitzvah).

(Gemara): Our Mishnah teaches 'from the time when Kohanim enter to eat their Terumah.'

(R. Chiya - Beraisa): It is the time when people enter to eat their bread on Shabbos night.

(Beraisa): Their words are close to the same.

Question: When Kohanim enter to eat Terumah is [right after the end of the] day. It is once the stars come out. The time when people enter to eat their bread on Shabbos night is [one or two] hours into the night, and you say that their words are close to the same?!

Answer (R. Yosi): [R. Chiya] discusses people of small villages. They leave [the Beis ha'Keneses in the field] while it is still day, due to [fear of] Chayos that lie in ambush.

(Beraisa): One who reads before this, he did not fulfill his obligation.

Question: If so, why do people read it in the Beis ha'Keneses [before this]?

Answer (R. Yosi): They do not read it in the Beis ha'Keneses to fulfill their obligation, rather, in order to enter Tefilah (Shemoneh Esre) amidst Divrei Torah.

(R. Ze'ira citing R. Yirmeyah): If it is a Safek whether one blessed on his food or did not bless, he must bless, for it says "v'Achalta v'Savata u'Verachta'' (it is a Torah Mitzvah);

If it is a Safek whether one prayed or did not pray, he does not pray (Tefilah is mid'Rabanan).

This is unlike R. Yochanan, for R. Yochanan said, 'if only a person would pray the entire day!'

What is the reason? There is no loss in Tefilah (it is request; there is no concern for Brachah l'Vatalah).

Question: If it is a Safek whether he recited or did not recite [what is the law? CHAREDIM - he is unsure whether Keri'as Shma is mid'Oraisa or mid'Rabanan.]

Answer: We learn from [the above Beraisa]. One who reads before this, he did not fulfill his obligation.

Before this (Bein ha'Shemashos), is it not a Safek? (If it is day, he was not Yotzei. If it is night, he was Yotzei.) And you say that [he was not Yotzei, and] he must recite [again]! This shows that if it is a Safek whether or not he recited, he must recite.

(Beraisa): A sign [of when day ends] is Tzeis ha'Kochavim. Even though there is not a proof, there is a hint to this - "va'Anachnu Osim ba'Melachah v'Chetzyam Machazikim b'Ramachim me'Alos ha'Shachar Ad Tzeis ha'Kochavim'' (they worked from dawn until Tzeis ha'Kochavim), and it says "v'Hayu Lanu ha'Lailah Mishmar veha'Yom Melachah.''