One of the basic tenet of Jiddu Krishnamurthy teachings was observer is observed. It means the observer is not different than the psychological states it observes. Below is one of the explanation -
If you understand this one radical principle, you will have understood something immense: that where there is an observer separating himself from the thing he observes, there must be conflict. Do what you will, as long as there is a division between the observer and the observed, there must be conflict. As long as there is division between the Muslim and the Hindu, between the Catholic and the Protestant, between the Black and the White, there must be conflict; you may tolerate each other, which is an intellectual covering of intolerance.
As long as there is division between you and your wife, there must be conflict. This division exists fundamentally, basically, as long as there is the observer separate from the thing observed. As long as I say, "Anger is different from me, I must control anger, I must change, I must control my thoughts", in that there is division, therefore there is conflict. Conflict implies suppression, conformity, imitation, all that is involved in it. If you really see the beauty of this, that the observer is the observed, that the two are not separate, then you can observe the totality of consciousness without analysis. Then you see the whole content of it instantly.
Now, so far I have not found any similar teachings in any religion. It's moreover seems contrary to every school of Vedanta including Advait Vedanta. But I have found a saying of Abhinavgupta which seems to say this once -
Attraction and repulsion, pleasure and pain, rising and setting, self-confidence and depression; all these states with which the universe is formed shine as mutually different but in reality they are not. Whenever you perceive the specificity of some thing, at that very moment you should perceive the essence of your own consciousness as one with it… why not take delight in the fullness of that awareness! Anuttarashtika v-5
But I wanted if any scripture directly or indirectly talks about this observer is observed?