Srimad Bhagavatam Canto 11, Chapter 28, Text 36

SB 11.28.36

etavan atma-sammoho
 yad vikalpas tu kevale
atman rte svam atmanam
 avalambo na yasya hi
Whatever apparent duality is perceived in the self is simply the confusion of the mind. Indeed, such supposed duality has no basis to rest upon apart from one’s own soul.
As explained in verse 33 of this chapter, the eternal self is neither assumed nor lost, since every living entity is an eternal reality. The word vikalpa, or “duality,” here refers to the mistaken idea that the spirit soul is partly composed of matter in the form of the gross body or subtle mind. It is thus that foolish persons consider the material body or mind to be an intrinsic or fundamental component of the self. In fact the living entity is pure spirit, without any tinge of matter. Consequently the false ego, which is generated by the false identification with matter, is a mistaken identity imposed upon the pure spirit soul. The sense of ego, or “I am” — in other words, the sense of one’s individual identity — comes from the spirit soul, because there is no other possible basis for such self-awareness. By studying one’s false sense of ego, one can analytically understand that there is a pure ego, which is expressed by the words aham brahmasmi, “I am pure spirit soul.” One can easily understand in a similar way that there is a supreme spirit soul, the Personality of Godhead, who is the omniscient controller of everything. Such understanding in Krsna consciousness constitutes perfect knowledge, as described here by the Lord.
Srimad Bhagavatam Canto 11, Chapter 28, Text 35
Srimad Bhagavatam Canto 11, Chapter 28, Text 37