One of the later Upanishads (12th century?), being part of the Atharva veda.
All the gods waited upon the Goddess (and asked): ‘Great Goddess, who are You ?’
She replied: I am essentially Brahman. From Me (has proceeded) the world comprising Prakriti and Purusha, the void and the Plenum. I am bliss and non-bliss. Knowledge and ignorance are Myself. Brahman and non-Brahman are to be known – says the scripture of the Atharvans. I am the five elements as also what is different from them. I am the entire world. I am the Veda as well as what is different from it. I am the unborn; I am the born. Below and above and around am I. I move with Rudras and Vasus, with Adityas and Visvedevas. Mitra and Varuna, Indra and Agni, I support, and the two Asvins. I uphold Soma, Tvastir, Pusan and Bhaga, The wide-stepping Vishnu, Brahma, Prajapati. To the zealous sacrificer offering oblation And pressing the Soma-juice do I grant wealth; I am the state, the Bringer of Wealth; Above it all, place I its protector. Who so knows my essence in the water of the inner sea, Attains he the Goddess’s abode.
From the translation by Dr. A. G. Krishna Warrier (Chennai: Theosophical Publishing House)  See also the prose summary in N.S.Subrahmanian, Encyclopedia of the Upanisads (New Delhi: Sterling, 1985):303-304.
French translation: Devi Upanisad, publiee et traduite par Jean Varenne (Paris: Adrien Maisonneuve, 1971), reviewed in the Journal of the American Oriental Society v93(3) 1973:375-376.