Srimad Bhagavatam Canto 07, Chapter 07, Text 23

SB 7.7.23

dehas tu sarva-sanghato
 jagat tasthur iti dvidha
atraiva mrgyah puruso
 neti netity atat tyajan
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
There are two kinds of bodies for every individual soul — a gross body made of five gross elements and a subtle body made of three subtle elements. Within these bodies, however, is the spirit soul. One must find the soul by analysis, saying, “This is not it. This is not it.” Thus one must separate spirit from matter.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
As previously stated, svarnam yatha gravasu hema-karah ksetresu yogais tad-abhijña apnuyat. An expert in the study of soil can find out where gold is and then dig there. He can then analyze the stone and test the gold with nitric acid. Similarly, one must analyze the whole body to find within the body the spirit soul. In studying one’s own body, one must ask himself whether his head is his soul, his fingers are his soul, his hand is his soul, and so on. In this way, one must gradually reject all the material elements and the combinations of material elements in the body. Then, if one is expert and follows the acarya, he can understand that he is the spiritual soul living within the body. The greatest acarya, Krsna, begins His teachings in Bhagavad-gita by saying:
dehino ’smin yatha dehe
 kaumaram yauvanam jara
tatha dehantara-praptir
 dhiras tatra na muhyati
“As the embodied soul continually passes, in this body, from boyhood to youth to old age, the soul similarly passes into another body at death. The self-realized soul is not bewildered by such a change.” (Bg. 2.13) The spirit soul possesses the body and is within the body. This is the real analysis. The soul never mixes with the bodily elements. Although the soul is within the body, it is separate and always pure. One must analyze and understand his self. This is self-realization. Neti neti is the analytical process of rejecting matter. By expertly conducting such an analysis, one can understand where the soul is. One who is not expert, however, cannot distinguish gold from earth, nor the soul from the body.
Srimad Bhagavatam Canto 07, Chapter 07, Text 22
Srimad Bhagavatam Canto 07, Chapter 07, Text 24