Brachot 8b

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"Until the end of the first watch": Rav Yehuda cited Shmuel 

the halacha is like Rabban Gamliel {in the Mishna that one can read Shema the entire night.}

We learn in a brayta: Rabbi Shimon ben Yochai says: there are times that a man reads Shema twice in one night, one before dawn breaks and one after dawn breaks and fulfill his obligation, both for {the Shema of} night and day.

Rav Acha bar Chanina cited Rabbi Yehoshua ben Levi: we rule in accordance with Rabbi Shimon ben Yochai. {and thus we would rule in accordance with the aforementioned brayta. The gemara continues:}

There are those that apply the statement of Rav Acha bar Chanina {citing Rabbi Yehoshua ben Levi} upon this that we learn in a brayta with Rabbi Shimon ben Yochai citing Rabbi Akiva that there are times than a person reads Shema twice in the day, one before the sunrise and once after the sunrise and fulfill his obligation both for day and night - Rav Acha bar Chanina cited Rabbi Yehoshua ben Levi: we rule in accordance with Rabbi Shimon ben Yochai.