Bhagavad Gita, Chapter 7, Verse 12

And whatever states pertaining to Sattva, and those pertaining to Rajas, and to Tamas, know them to proceed from Me alone; still I am not in them, but they are in Me.

The source of something and being contained by it turn out to be two genuinely different things.

This makes a careful, real distinction. These three qualities that shape material life all originate from the same source described throughout this chapter, but that source itself isn't limited or defined by any of them.