Bhagavad Gita · Chapter 13: The Field and the Knower of the Field
Bhagavad Gita 13.4
ऋषिभिर्बहुधा गीतं छन्दोभिर्विविधैः पृथक् ।
ब्रह्मसूत्रपदैश्चैव हेतुमद्भिर्विनिश्चितैः ॥
ṛṣibhirbahudhā gītaṃ chandobhirvividhaiḥ pṛthak | brahmasūtrapadaiścaiva hetumadbhirviniścitaiḥ ||
This has been sung by the seers in many ways, in various distinct hymns, and also in the well-reasoned and conclusive words of the Brahma Sutras.
Modern context
Krishna points to his sources: the seers have sung this in many ways, and it has been reasoned out carefully in the Brahma Sutras. He is not claiming the idea is new. He is placing it in a long tradition, both poetic and philosophical. The deepest truths are usually not invented by one person; they are discovered and rediscovered by many.