פירוש על ברכות 3:8

Two deductions are drawn from the verse : (1) The law of reading the Shema' since the Israelite is commanded "to talk of them" (viz. "these words which I command thee this day") on lying down and rising up ; (2) The right order is "lying down" and "rising up," i.e. evening and morning.

On the text it is based - And there you can learn the obligation of reading (Shema)