Savitri Upanishad is one of the 108
Upanishads. It is a minor Upanishad and belongs to the Sama Veda.
Savithri Upanishad mentions about pairs existing in nature. Male concept is called Savitar, and the female is Savithri. Thus air/ether, thunder/lightening, moon/stars, man/woman all exist as pairs in nature. Savithri Upanishad mentions the human mind to be Savitar, and the whole universe its corresponding pair, Savitri.