There is a verse in the Brihadaranyaka Upanishad which says,
Indra, through Maya, appeared as many forms. [1]
It has been quoted by both Gaudapada and Shankara to illustrate how, through the illusion of Maya, Brahman appears as many. With knowledge of Advaita, this illusion is dispelled.
The full verse says,
He shifted shape to match every shape, to manifest his shape. Indra, through Maya, appeared as many forms. his horses, hundreds and ten, are yoked.
Though quoted in Advaita literature, the verse is, itself, a quote — from the Rig Veda [2].