Ashtavakra Gita

Only the ignorant see the world as a duality; the wise see everywhere only the self

The "duality" being rejected here is specifically the split between a conscious knower and an unconscious world, not the ordinary variety among things perceived.

"Duality" in this verse does not mean noticing that the world contains many different things — the Gita nowhere denies that a tree differs from a river or that one person differs from another in appearance. It means, more specifically, treating the knower and the known, self and world, as two fundamentally separate kinds of existence, one conscious and one not. The wise, by this verse's account, do not stop perceiving variety; they simply no longer draw that particular line, since every object of perception is recognized as arising within, and never separate from, the one awareness perceiving it. Chapter 2's repeated declarations, from the sky-and-pot image through the clay-and-pot analogy to this line, are converging on the same single discrimination approached from several directions: form varies, substance does not.

Ashtavakra Gita