Bhagavad Gita, Chapter 14, Verse 27

For I am the abode of Brahman, the Immortal and Immutable, of everlasting Dharma and of Absolute Bliss.

The chapter closes by naming what stands behind even the formless Brahman, one real, single source.

Krishna doesn't present Brahman as a separate, higher reality, he names himself as its actual basis. Real unity closes the chapter, tying everything discussed back to one source.