From the Torah:

And these words, which I command thee this day, shall be upon your heart;  and thou shall teach them diligently unto your children, and you shall talk of them when thou sit in your house, and when thou walk by the way, and when you lie down, and when you rise up. And thou shall bind them for a sign upon your hand, and they shall be for frontlets between your eyes. And thou shall write them upon the door-posts of your house, and upon your gates.
Deuteronomy 6: 6-9

For this commandment which I command you this day, it is not too hard for thee, neither is it far off.  It is not in heaven, that you should say: 'Who shall go up for us to heaven, and bring it unto us, and make us to hear it, that we may do it?' Neither is it beyond the sea, that you should say: 'Who shall go over the sea for us, and bring it to us, and make us to hear it, that we may do it?' But the word is very near to you, in your mouth, and in your heart, that you may do it.
Deuteronomy 30:11-14