Bhagavatapurana 2.9.35

2.9.35

etāvadeva jijñāsyaṃ tattvajijñāsunātmanaḥ /
anvayavyatirekābhyāṃ yat syāt sarvatra sarvadā //

35. By one who is intent upon knowing the truth of Atman, only this much is necessary to be enquired into and understood that Atman is the thing which exists at all places and in all times, as being connected with all effected things as their cause and as being different from them in the causal state, or as being a witness in the states of wakefulness, dreaming and sleep, and as unconnected with anything else in samadhi and other higher states [by positive and negative arguments or rather relations.]