Chandogya Upanishad is part of the Sama Veda. There are eight chapters in it. Here are few quotes from Chandogya Upanishad:
Previous to creation all this was being, one only without a second, Name and form were not.
Just as by one clod of clay all that is made of clay is known, the modification being only a name, arising from speech, while the truth is that all is clay.
Just as by one nugget of gold all that is made of gold is known, the modification being only a name, arising from speech, while the truth is that all is gold.
Where one sees another, one hears another, so long as there are two, there must be fear, and fear is the mother of all misery. Where none sees another, where it is all one, there is none to be miserable, none to be unhappy.
Through purity of food comes purity of mind, through purity of mind comes a steady memory of Truth, and when one gets this memory one becomes free from all knots of the heart.