KENA UPANISHAD 3:4 [who is this?]

That was approached by it, but it was asked: who is this? Fire indeed, I am this, it said: all-knowing, indeed, I am this.

tad abhyadravat tam abhyavadat ko 'sity agnir va aham asmity abravij jata-veda va aham asmiti.

Note: here begins the all-important inquiry, and thus it is important to emphasize the 'roles' of That and this, as well as to note, despite its (this) approach, That initiates the inquiry. Also note the self-contained response.