Halakhah zu Bamidbar 23:24

The law of the recitation of Shema morning and evening: That we were commanded every day, morning and evening, to read one verse from the Torah in this Order, and that is "Hear Israel, the Lord is our God, the Lord is one" (Deuteronomy 6:4). And about this verse is it stated (Deuteronomy 6:7), "and you will speak in them in your sitting in your home, in your laying down and in your rising up." And the explanation about this comes (Berakhot 10b) [that it is] at the time that people lay down and at the time that people get up. And it is established to us for the Rabbis (Berakhot 10b) that all of the night until the dawn rises is called the time that people lay down - and like the matter that is written (Leviticus 26:6), "and you will lay down and there is no one that makes to tremble"; and so [too], "it does not lay down until it eats prey" (Numbers 23:24) - since all the time of its laying down is implied. And also that people are divided in their attributes regarding laying down. There are those that do not lay down until half of the night, and some [not] until its end, and there are some that lay down immediately at the beginning of the night. And because of this, they said (Berakhot 10b) that the time of the recitation of Shema at night is from the time that the priests retire to eat their priestly tithe - which is the coming out of the stars - until the dawn rises. And the time that people rise up was understood [by] them [to be] from the beginning of the day - meaning to say when the morning is light [enough] that a man can recognize his fellow from the distance of four ells - until three full hours (Mishneh Torah, Laws of Reading the Shema 1:11). And rising up was not understood by them to be all of the day, like laying down; as it is not the way of any person that is healthy to rise up from his bed at the end of the day, or even its middle. And they, may their memory be blessed, said (Berakhot 9b) about the recitation of Shema of the morning that, in any case, from here onward - meaning from the end of three hours until the end of the day - he who did not read [it] did not lose [out] that he not be able to read it with its blessings.