Chandogya Upanishad 1.7

Now with reference to the body. Rik is speech, Sâman breath. This Sâman (breath) rests on that Rik (speech). Therefore the Sâman is sung as resting on the Rik. Sâ is speech, ama is breath, and that makes Sâma.

Rik is the eye, Sâman the self. This Sâman (shadow) rests on that Rik (eye). Therefore the Sâman is sung as resting on the Rik. Sâ is the eye, ama the self, and that makes Sâma.

Rik is the ear, Sâman the mind. This Sâman (mind) rests on that Rik (ear). Therefore the Sâman is sung as resting on the Rik. Sâ is the ear, ama the mind, and that makes Sâma.

Rik is the white light of the eye, Sâman the blue exceeding darkness. This Sâman (darkness) rests on the Rik (brightness). Therefore the Sâman is sung as resting on the Rik. Sâ is the white light of the eye, ama the blue exceeding darkness, and that makes Sâma.

Now the person who is seen in the eye, he is Rik, he is Sâman, Uktha, Yagus, Brahman. The form of that person (in the eye) is the same as the form of the other person (in the sun), the joints of the one (Rik and Sâman) are the joints of the other, the name of the one (ut) is the name of the other.

He is lord of the worlds beneath that (the self in the eye), and of all the wishes of men. Therefore all who sing to the vînâ (lyre), sing him, and from him also they obtain wealth.

He who knowing this sings a Sâman, sings to both (the adhidaivata and adhyâtma self, the person in the sun and the person in the eye, as one and the same person). He obtains through the one, yea, he obtains the worlds beyond that, and the wishes of the Devas;

And he obtains through the other the worlds beneath that, and the wishes of men. Therefore an Udgâtri priest who knows this, may say (to the sacrificer for whom he officiates);

"What wish shall I obtain for you by my songs?" For he who knowing this sings a Sâman is able to obtain wishes through his song, yea, through his song.