Berachot 9a

[Berachot 9a]
Rabbi Achar bar Chanina cited Rabbi Yehoshua ben Levi: The halacha is like the words of Rabbi Shimon who spoke in the name of Rabbi Akiva.

And like this sugya does the Rif explain as well.

 Rabbi Zera said: so long as he does not say Hashkiveinu - {"who causes us to lie down"}

Rashi explains: One who reads Shema of night at Shacharit close to break of dawn [amud hashachar] should not say hashkiveinu, for this is not now the time of the beginning of lying down, but rather the end of lying down.

And there are those who explain that this applies only to he who read after break of dawn [sheyaaleh amud hashachar], but after break of days, he is able to say hashkiveinu. And so is implied from the establishing the place of the citation of Rabbi Zera after the brayta of Rabbi Shimon ben Yochai.

And Rabbi Yitzchak Gaus za'l wrote that this does not mean that he should not say the entire bracha, for behold he needs to say two [blessings] after it [Shema]. Rather, he should not say those words Hashkiveinu Hashem Elokeinu leShalom, but rather he should begin vetakeneinu be'eitza tova milefanecha.

And it does not seem to be as he explained, for if so, the gemara should have explained it as later on in the second perek (daf 14b) where it states 'where he should not say Ani Hashem Elokeichem, he does not need to say Emet', and the gemara explains how to say the bracha.

Mishna: ONCE IT HAPPENED THAT HIS SONS CAME HOME [LATE] FROM A WEDDING FEAST AND THEY SAID TO HIM: WE HAVE NOT YET RECITED THE [EVENING] SHEMA'.
HE SAID TO THEM: IF THE DAWN HAS NOT YET COME UP YOU ARE STILL BOUND TO RECITE.

AND NOT IN RESPECT TO THIS ALONE DID THEY SO DECIDE, BUT WHEREVER THE SAGES SAY 'UNTIL MIDNIGHT', THE PRECEPT MAY BE PERFORMED UNTIL THE DAWN COMES UP.

THE PRECEPT OF BURNING THE FAT AND THE [SACRIFICIAL] PIECES, TOO, MAY BE PERFORMED TILL THE DAWN COMES UP.
SIMILARLY, ALL [THE OFFERINGS] THAT ARE TO BE EATEN WITHIN ONE DAY MAY LAWFULLY BE CONSUMED TILL THE COMING UP OF THE DAWN.
WHY THEN DID THE SAGES SAY 'UNTIL MIDNIGHT'?
IN ORDER TO KEEP A MAN FAR FROM TRANSGRESSION.

Gemara: And yet, the Mishna does not teach regarding eating the korban Pesach and Hallel during the night of Pesach.

And I will oppose [this implication with this brayta]: The duty of the recital of the Shema' in the evening, and of the Hallel  on the night of the Passover, and of the eating of the Passover sacrifice can be performed until the break of the dawn [ad sheyaaleh amud hashachar]?

Rav Yosef said: There is no contradiction. One statement [the Mishnah] conforms with the view of Rabbi Eleazar ben Azariah, and the other with the view of Rabbi Akiva.

For they taught [in a brayta]:
{Shemot 12:8}:

ח  וְאָכְלוּ אֶת-הַבָּשָׂר, בַּלַּיְלָה הַזֶּה:  צְלִי-אֵשׁ וּמַצּוֹת, עַל-מְרֹרִים יֹאכְלֻהוּ.

8 And they shall eat the flesh in that night, roast with fire, and unleavened bread; with bitter herbs they shall eat it.

Rabbi Eleazar ben Azariah says: Here it is said: 'in that night', and further on it is said {pasuk 12}:

יב  וְעָבַרְתִּי בְאֶרֶץ-מִצְרַיִם, בַּלַּיְלָה הַזֶּה, וְהִכֵּיתִי כָל-בְּכוֹר בְּאֶרֶץ מִצְרַיִם, מֵאָדָם וְעַד-בְּהֵמָה; וּבְכָל-אֱלֹהֵי מִצְרַיִם אֶעֱשֶׂה שְׁפָטִים, אֲנִי ה.

12 For I will go through the land of Egypt in that night, and will smite all the first-born in the land of Egypt, both man and beast; and against all the gods of Egypt I will execute judgments: I am the LORD.

Just as the latter verse means until midnight, so also here it means until midnight.

Rabbi Akiva said to him: But it is also already said {pasuk 11}: 

יא  וְכָכָה, תֹּאכְלוּ אֹתוֹ--מָתְנֵיכֶם חֲגֻרִים, נַעֲלֵיכֶם בְּרַגְלֵיכֶם וּמַקֶּלְכֶם בְּיֶדְכֶם; וַאֲכַלְתֶּם אֹתוֹ בְּחִפָּזוֹן, פֶּסַח הוּא לַה'.

11 And thus shall ye eat it: with your loins girded, your shoes on your feet, and your staff in your hand; and ye shall eat it in haste--it is the LORD'S passover.

Until the time of haste {and they hastened out of Egypt at the break of dawn -- see Shemot 12:22}. If so, what is it teaching with בַּלַּיְלָה? That perhaps it could be eating like kodshim, which are eaten in the day. Therefore it teaches us בַּלַּיְלָה. At night it is eaten and it is not eaten in the daytime.

And the setama of the Mishna {meaning without specific attribution, but the plain narrative voice} of here goes according to Rabbi Eleazar ben Azaria, and so does the setama of the Mishna at the end of Pesachim (daf 120b), and so too the setama of the Mishna of Eizehu Mekoman (daf 56b).

And one should not deduce from these setamas that the halacha is like Rabbi Eleazar ben Azarya, for there is also stated in Megillah (daf 20b) the setama like Rabbi Akiva. And we sat in perek Mitzvat Chalitza (daf 101b) what is the difference between one or two setamas?

And so too, one should not deduce that the halacha is like Rabbi Akiva from how they taught as a paskened halacha in Megillah. For it not comparable to this of haSocher et haUmnin (Bava Metzia daf 96a) that 'anyone who retracts, his hand is on the bottom', for there, they teach together things which are comparable to one another, (even though) anyone who changes, he has the lower hand, it is not its place to teach there, but by way of saying kol hachozer he mentioned it, but there, he taught all together 'all whose time is at night. Just the opposite, this of Eizehu Mekoman appears more as a paskened halacha, for behold they taught in that very Mishna the time of kodshim. And according to the sefarim that are gores later on 'and these Tannaim are like these Tannaim', and establish Rabbi Yehoshua like Rabbi Akiva, it is implied a bit that the halacha is like Rabbi Akiva.

And since we are in doubt in accordance with whom the halacha is, we need to be stringent to eat matza of the afikoman before Chatzot, as is stated in Pesachim (daf 120b) that according to Rabbi Eleazar ben Azariah one needs to eat the obligatory matza before Chatzot.