It is also stated in the Midrash (Yalkut Shimoni Parshat Vayechi, Remez 157) in the following language: "And Jacob called to his sons" (Genesis 49:1) - Jacob wished to reveal to his sons the end of days, but the Divine Presence departed from him. He said, perhaps there is a flaw in my offspring, like Abraham my grandfather, from whom Ishmael came forth, and like Isaac my father, from whom Esau came forth. They said to him: "Shema Yisrael, etc.," just as there is only one in your heart, so too in our hearts there is only one. Immediately he opened and said: 'Blessed be the name of His glorious kingdom forever and ever,' thus far.

And this is the language of the Rambam (Chapter 1 of Hilchot Kriat Shema, Halacha 4): It is a tradition in our hands that when our father Jacob gathered his sons in Egypt at the time of his death, he commanded and urged them regarding the unity of God and the way of the Lord that Abraham and Isaac his father followed. And he asked them and said: My sons, perhaps there is among you someone who is flawed, who does not stand with me in the unity of God, etc. They all answered and said: "Shema Yisrael, Hashem Elokeinu, Hashem Echad," meaning, hear from us our father Israel, Hashem is our God, Hashem is one. The elder opened and said: 'Blessed be the name of His glorious kingdom forever and ever,' thus concludes the Rambam's words.